The Basics
One player starts by passing a "zip" to another player, this is done through a motion with the hand and eye contact. The next player does the same, except he says "zap", the next player says "zop" and this repeats until someone makes a mistake.
Variations
Instead of passing a "zip" after being "zopped" by another, one can change the beginning of the word zip to make it a word that rhymes with zip. For example crip, trip, prip, stip, then the following player would have to say crap, trap, prap, or stap respectively and so on and so forth.
Another variation is instead of saying zip is to say any word, such as "tree" the next two players must think of words that correspond with tree such as "grass" and "flower", the fourth player would then finish this segment by saying plant life and pointing to someone who would there in turn go back to zipping.