Throw in, get more back
Snapback is a one-stone sacrifice with a guaranteed refund. You throw a stone into the enemy's two-space eye; it has a liberty there, so the play is legal, and White has no choice but to capture it — but capturing fills White's own eye and leaves the whole ring on a single liberty. You recapture at once and collect everything. The preconditions: a group already short of liberties, and an eye space small enough to be spoiled by its own capture — the two-space eye is the classic victim, while a three-space eye usually survives. Missing a snapback is expensive; seeing one changes how you value every almost-captured group. Black to play: throw in.