Author Larry Callen is carrying a big, battered blue suitcase, and all the kids sitting on the floor of the Cheshire Cat Bookstore want to know what's inside.

"It's a tall tale but it's kind of squished," answers Callen, who is here to talk about his own books and to tell kids how to write their own tall tales for a contest the children's bookshop is sponsoring.

In a tall tale, says Callen, "the truth is kind of stretched out."

"Some tall tales are about people outsmarting machines -- like John Henry -- or people conquering the wilderness -- like Paul Bunyan," begins Callen.

"Another tall tale is about Robin Hood," interrupts a child.

Callen's personal rule about tall tales is that they have to be funny and they have to be written "like the way you talk." Opening the mysterious suitcase, he pulls out a placard with just two words written on it: what if? Those two little words, Callen says, keep tales spinning. To illustrate, he stages a play, using volunteers from the audience as actors. The name of the play, he tells them as he pulls another placard from his suitcase, is "The Cheshire Chicken."

What if, asks Callen, this big, tough 30-pound chicken pounces on a cat?

"The dog could come along and try to save the cat by jumping on the chicken," answers a boy.

Callen likes the image of a cat sandwich, but says that "something funny has to happen."

"A pig could come along and eat the cat sandwhich," tries another child.

"Or it could start raining cats and dogs so there would be more cats and dogs than chickens," someone else suggests.

"Or someone in the audience could just yell 'lunch break' and they'd stop fighting," says a little boy.

The play ends without really concluding, but Callen is satisfied that the kids have the idea.

"This is the way I write," he tells them. "I keep this 'what if' sign on my office wall, and I keep asking myself what if, what if a dog comes along. . ."

One of Callen's books, The Deadly Mandrake, asks what if you want to pull up a deadly mandrake root without killing a skinny dog. Deadly mandrake root isn't readily available, so Callen pulls a substitute prop out of the blue suitcase -- a piece of giner root carved into a doll-like shape.

"If there's a dealy mandrake root in the ground, all sorts of bad things happen," begins Callen.

"Like spiders in your bed?" asks a boy.

"Yes, but if you get the root out of the ground the right way it will stop the bad luck," he continues. "But if you do it wrong, you'll drop dead. So I loosened the ground around the root with a stick and tied some twine to the root and tied the other end of the twine around the neck of a skinny dog. Then I decided I didn't want the dog to die, so I asked 'what if' again. Any ideas?"

"You could get another skinny dog," suggests a girl.

"You could tie it to a truck," suggests a boy.

"But the truck would get stuck in your backyard," says another kid.

"Instead of a dog you could use a skinny rat' cause no ones likes rats," answers another child.

"Well, my 'what if' turned out differently," Callen tells them. "The string broke and the skinny dog ran away. Then a cow came along and pulled up the mandrake root. But the cow didn't die. Do you know why? I just made a law, Callen's law. Mandrakes can't kill old gray cows.

"With stories, what you want to happen happens. You can save the lives of skinny dogs and old gray cows. You can take the truth and stretch it till it pops like a rubber band. Now does anybody have an idea for a tall tale?"

"I know one about a chicken and a giant and it's from the library," says a little girl. "The giant takes the chicken's eggs. But the chicken swallows a big lake and then she tumbles on the giant and he's got seaweed coming out of his nose!"

"What about another way to get mandrake out of the ground?" asks a girl with rosy cheeks and pretty blonde hair.

"You don't have to write about things I write about," says Callen. "Write about a girl with rosy cheeks and pretty blonde hair.

In the writing contest, preliminary indications are that contestants will be following the age-old dictum to write about things they know. The two entries received at the bookstore the day the contest opened both appear to draw heavily on contemporary culture. One is about a female tennis champ and one focuses on a pair of characters named Pillsbury Pop and Fresh Dough.