Ernie Hempel stood at the side of the sign that said Toilet Train Your Cat and re-ran the "Real People" cassette once more with feeling. Through the magic of videotape, there was Ernie on the wide screen, telling America how he toilet-trained his cat; there was Ernie placing the plastic shield filled with his "special herbs" kitty litter under the toilet seat in his own bathroom so it fit just right. Then, there was his cat, a brown-and-white tiger-stripe, jumping onto the seat. Looking into the camera, half-smiling, and actually doing it, right into the bowl. And then, there was Ernie's cat scratching at the back of the seat -- unbelievable! -- triggering the flush mechanism, flushing the toilet.

Cat potties are Ernie Hempel's business.

(Hey, it's tough work but somebody's got to do it.)

They retail his "single cat" model for about $15 and his "two cats together, or one big cat" model for about $17. His Brite Ideas toilet kits come neatly packaged in plastic, and he says they are foolproof.

But can any cat really learn to play?

Listen to old Ern: "You stick your cat in the bathroom. You close the door. By morning, he's using the toilet."

And Ernie's not resting. He's got the fever, he's hot, he cannot be stopped.

"I'm working on one for dogs too."

This is what it comes to in 1980: the cat potty. The water bed for dogs. The hamster condominium. The Catanooga Choo Choo and tree house for cats. The mink bed. The brass bed. The greeting cards. The designer T-shirts. The jerky-coated waffle. These items are among what's hot at the 22nd annual American Pet Products Manufacturers Association convention that ends today at the Sheraton.

Pet products, in case you didn't know, are said to be the nation's fourth-largest industry. According to industry statistics, pet food alone was a helluva lot bigger than baby food; it isn't even a close run," said Al Simon, whose company, Four Paws, manufactures sanitary napkins for dogs and cats, among other equally essential products. By 1982, fish supplies -- not fish food, just aquarium supplies -- are expected to do close to $2 billion.

Chicken feed though it partially may be, chicken feed it ain't.

"My friends drive Chevys," Simon said. "I drive a Mercedes. Does that answer your question?"

A lot of white shoes. A lot of white belts. A lot of spread collars and three-piece suits with reversible vests and two pairs of coordinated slacks. The full cleveland look. And at one time or another just about all of them came to see Al Simon at Four Paws booth. Simon is New York all the way, and he doesn't mind calling attention to himself, from the gold jewelry to the Adolfo threads to the personalized license plates that say -- WEE WEE. That's an inside joke. Stands for the Wee Wee pad, Four Paws' biggest seller. It's a pad with an attractant scent for the dog owner who'll do anything for his dog but walk him. It's disposable and absorbent. What it is, is a floor-bound Pampers. Four Paws also makes cologne -- "smells like Chanel; you could give it to your girlfriend, or your girlfriend's dog" -- and sanitary napkins for animals. Soon Four Paws will come out with still another first -- feminine hygiene spray for dogs.

Do dogs buy these.

No. Dog owners buy these. When was the last time you saw a beagle waving a twenty?

"Everything sells," Simon says. "It's all in the packaging. I'm no genius, but I package good. Look, could you figure Wee Wee pads? It's a joke, right? But they retail eight to the box for $2.49, and that means that people are spending over 30 cents each time their dog has to urinate. Think about it."

Eight years ago they laughed at Al Simon when he quit the carpet business.

They laughed at him because all he had was a spray bottle of dog cologne and a dream. Now he has a Mercedes, a million dollars, a male Great Dane -- and a "hamster ball," a clear plastic ball with a door on top to stick the hamster in so he can roll around like a marble.

And will hamsters like the hamster ball?

Al Simon shrugs his shoulders inside his perfectly cut suit as if to say How the hell do I know what a facockta hamster will like?

"It's brand, spankin' new," said Anne Hollander, inside the Johnson Pet-Dor booth. "It" being the water bed for dogs. A bag of water, encased between two layers of foam rubber, covered by lamb's wool. The small one will retail for about $39 and the large one for about $59. Anne Hollander is very excited about this product. She says it's natural for people who sleep on water beds to buy water beds for their dogs. She is, you may have guessed, a Californian.

"Dogs love it," she says. "It's very therapeutic. It's especially good for dogs with arthritis -- they need a bed like this. I'll tell you this, if every dachshund owner bought one when his dog was a puppy we could save a lot of back problems."

Anne Hollander has seen a lot of pet products. She knows what's silly and what isn't.

"The Kitty potty," she says. "That's silly."

The water bed for dogs, on the other hand, "has therapeutic value."

Overheard at the convention:

"This product is unique."

"We call it The Skyline Duplex. It's three clear plastic rooms. An exercise room. A bedroom. And a skylight area to climb in. It's actually a hamster condominium. Absolutely unique."

"Dogs love it."

"Breath spray for dogs isn't silly. You want to know what's silly? Parasols for dogs are silly. Toothpaste for dogs is silly. But how can you say that breath spray for dogs is silly? Don't you want his kiss to taste sweet?"

"I don't know. I think nail polish for dogs is silly, but that beef-flavor toothpaste for dogs makes sense. Maybe I'm prejudiced because my father's a dentist, but brushing your teeth isn't silly."

"Cats love it."

"Jerky is the hot flavor now. You could coat shoe leather with jerky and dogs would eat it. We've jerky-coated Stella D'Oro bread sticks. The dogs are in seventh heaven."

"Do I love my dog? Of course I love my dog. When my kids have headaches, I talk to them, but when my dog has a headache, we go straight to the vet. Now, is that love?"

"Fish love it."

"No, you don't spray this on the poop to liquify it. You bring the poop to the drum you've sunk in the ground, drop it in, and then the chemicals in this liquefy it. Son, if we could get the dogs to do it right into the drum we'd be millionaires."

"Some of these laws are poorly written. Say a state says you have to inoculate every animal -- how are you going to inoculate a goldfish?"

"I don't have to try it. I sell it, pal. I don't eat it."

"Birds love it."

"You got 44 million pet birds. You got 75 million pet dogs and cats. Now, you wanna talk big numbers? Then let's start talking FISH."

"It's a unique product."

Anything you sell is a unique product. Anything he sells is silly. But if it sells, so what? This is America.

The $4,000 gold-plated finch cage.

The $35 dog or cat carrier with the outside painted to look like a London bus.

The quarter-pounder Old Mother Hubbard dog biscuit, the Famous Amos of dog biscuits.

The $50 Cat-anooga Choo Choo, a "cat tree house" made of three different colors of thick, scratchable carpet, shaped like a train with a sleeping carpet, and a carpet mouse hanging from a carpet string. Very functional.

The $40 brass bed for toy poodles. Very therapeutic.

The $15 clear plastic doggie raincoat. Very necessary.

"Believe it or not," says Dora Krachey, "there are very large dogs that are pneumonia-prone."

Guess what she sells?

Dog jackets.

Very chic.

Sandy Landsbaum and Pat Shreves brought their Pet-A-Gram line of greeting cards a long way, from St. Louis.All sorts of cards for pets to send to other pets. Happy Birthday. Birth announcements and congratulations. Sympathy. Christmas. Little kitty sicky? Doggone, the dog's gone. Heard you had THE (neutering) operation? They say some people actually have their pets put their pawprints on the cards. So far, they haven't had any negative comments on their cards. A few people have told them they could make $100,000 selling them.

"I started it," Sandy says, "because I was a pet groomer -- I still do it twice a week -- and I needed to send these kind of cards to my clients. Like when someone had a litter, or when a customer died. I mean, an animal customer. Well, no one made the cards I needed. So I do now."

Sandy Landsbaum knows what's silly.

Nail polish for dogs.

"Listen, I had this one goddamn white poodle whose nails I used to have to paint red once a month. I wasn't even wearing polish, and I'm doing this goddamn dog in red. She'd actually hold her paw out still. Never move an inch. Ooooooh, I hated that dog. She died at 17. I sent a sympathy card. My own line."

Alan Zelinger sells the line of Ethical Products. Things like dog jackets. In denim, leopard skin, Sherpa fleece, Aztec and naval motif. Dog jackets with matching pompon caps. He also sells plastic boots for dogs, so they won't get their itty-bitty paws hurt by rock salt. And ski togs for dogs. And designer T-shirts for dogs, things that say "Pierre Cardog." He shows them on racks, just like on Seventh Avenue. Bright colors. Reds. Greens. Yellows. Oranges. The summer line. He likes to deal in ensembles, "so the gal walking down Connecticut Avenue can dress just like her dog."

He says in the business they call it "humanizing." He says, "People tend to humanize their pets. They love them like humans, and they think of them as humans, so they dress them as humans. Look, we all know that dogs don't give a damn if they eat hamburgers or cheeseburgers. But people do. And isn't Gaines making a mint with cheeseburgers for dogs? Of course now, our products are unique. Dogs need coats. You take a dog and domesticate him, make him a lap dog, make him accustomed to apartment life and you've acclimatized him. He just cannot go out in the cold without a jacket or sweater. You aren't being silly buying our line, you're being kind. If we are speaking about garments, about dog apparel, I'd say over a million garments are sold per year."

Garments? Dog apparel?

Alan Zelinger smiles.

"There's just no limit," he says.