A high-level technique for enforcing correct behavior in a protocol. Roughly speaking, Alice sends {$n$} items (e.g., garbled circuits), Bob asks for some number of them to be "opened", so they can be checked for correctness. If all of the opened items are deemed valid, then Bob has a statistical guarantee about the number of unopened items which are correct. Hence, the unopened items can be used in some way for the remainder of the protocol.