It's called the Memory Shtick, and it involves memorizing the following ten lines. Once you know them, the fun begins. You call a kid out of the audience to stand up in front of everyone. He/she must repeat each line after you, reciting all of the lines before it. So, you'll say line 1; he says line 1. You say line 2; he says line 1 and line 2; you say line 3; he says lines 1, 2, and 3. And so on. Enjoy!

One hen.
Two ducks.
Three squawking geese.
Four corpulent porpoises.
Five limerick oysters.
Six pairs of Don Alverso's tweezers.
Seven thousand Macedonian soldiers dressed in full battle of array.
Eight brass monkeys from the ancient sacred crypts of Egypt.
Nine sympathetic apathetic diabetic old men on rollerskates with a marked propensity toward procrastination and sloth.
Ten diabolical denizens of the deep who haul the maul and crawl the quay all around the block at the same time at the break of day.

(by Bill Cosby,) from: http://www.jewishyouth.com/issues/idea016.htm