All party givers play tricks, whether it is blending two or three cans of Campbell soup together and designating the result an old family recipe, or asking a single he and a single she for dinner in the hopes that they will depart a couple.

There are men and women, the caterers confide, who insist that all signs of outside intervention be removed before their guests arrive, and who then boldly take credit for the noisettes of lamb nestled in mint and the fruit sorbet. There are store-bought tarts pried from their tinfoil containers and served up on the family china by a hostess who assures everyone that making the tart was no trouble at all.

There is the bathroom lightbulb switched from a glaring 150-watt to a soft and diffuse pink or amber so that when the guest looks in the mirror he is flattered by the self who stares back. There is the gentle lie when, calling someone at the last minute to fill a suddenly empty spot at the table, you imply that you have been trying to reach the person -- most desirable of all guests -- for days.

Paltry pretenses that smooth the social passage; they are all too minor for April Fool's Day. To find tricks for today, we must go back in history to a time when culinary deception was practiced with an ardor and skill that assured that nothing was quite what it seemed.

"These cookes," complained Chaucer, "how they stampe and streyn, and grynde/And turnen substance into accident." Back then, turning substance into accident may have been the only way to endure a diet which, particularly during the winter, was severely limited.

But if you couldn't fool the tummy, you could at least fool the eye.

The pie with the unexpected filling was as big a source of amusement to the medieval host as the exploding cigar is to today's practical joker. Four and 20 blackbirds baked in a pie was more than an image out of a nursery rhyme.

"Make the coffin [crust] of a great pie or pasty," directs an early cookbook, "in the bottome thereof mak a hole as big as your fist . . . put into the said coffin . . . as many small live birds as the empty coffin will hold . . . set before the guests, where uncovering or cutting up the lid of the great pie all the birds will flie out . . ."

Sometimes it was frogs and their release would "Cause the ladies to squeak and hop about," according to Robert May, whose 1660 cookbook was big on such culinary tricks.

You will not want to fill your pie with live birds and frogs (unless, of course, you are under 10), but you could use the same principle to fill a pie with more socially acceptable surprises.

To produce the "coffin," bake the bottom crust filled with beans or pie weights to keep it from buckling, and bake the top crust separately, formed over the bottom of another pie dish or a lid of appropriate size. Fill the crust with favors or fortunes or penalties for the April Fool. Cover it with the pastry lid and serve it forth.

Walnuts were another favorite fooler, the shells carefully pried apart, the nut meat removed and something unexpected popped inside. One cook devised a way of baking biscuits inside the walnut shell; but the effort far exceeded the result.

Instead, pry the shell open, fill the walnuts with cashews or almonds or chocolate truffles and carefully glue the shells back together. Set them out in a bowl and watch what happens when the first guest wields the nutcracker.

Using turkey, chicken and quail, one could also produce a version of this Yorkshire Christmas pie from a 16th-century English cookbook:

"First make a standing crust, let the wall and bottom be very thick: Open the turkey, goose, fowl, partridge and pigeon all down the back, and bone them . . . season them all well first, and lay them in the crust (one inside the other), so as it will look only like a whole turkey . . ."

This crust, as in the pie designed to hold birds, frogs or favors, is not meant to be eaten; it is a case, to hold and hide the contents, and when the recipe says the walls should be "very thick," it means it.

That same age produced this bit of pomme foolery. Meatballs of ground pork or beef were mixed with currants and spices, shaped into large balls and roasted on a spit. Then they were dredged in a mixture of parsley, flour and beaten egg so that, when served, they looked like green apples. Alternately, parsley was replaced with saffron to produce golden "apples," hence the dish's name, pomme d'orres.

Or perhaps you'd prefer a phony pear, shaped from forcemeat but concealing a tiny roast bird, whose leg sticks out the top to form the stem. (Oh well, cooks got carried away then, too.)

Since this year Easter hops along right after April Fool's Day, serve the apples and pears with an egg as big as the Ritz. If no one eats it, haul it out again next week for Easter.

"To make an Egg as big as Twenty," Hannah Glasse wrote in her 18th-century cookbook, "part the yolks from the whites, strain them both separate through a sieve and tie the yolks up in a bladder in the form of a ball. Boil them hard. Then put this ball (having removed its bladder) into another bladder and the whites around it and tie it up in oval fashion and boil it. These are used for grand salads."

And a grand April Fool.