Sometimes video game developers want to get you to make a big leap of logic in an elegant way. An "antepiece" is a tiny little thing that precedes a great-big-difficult-challenge, and gives you subtle hints about how you should deal with the thing that's about to confront you.
An easy example is an early physics puzzle in Half-Life 2. There are a bunch of slugs on the ceiling with their tongues [...] [tvtropes.org]