Black pins the White Knight on KB3 by his QB. But the pin is conditional. Can White execute a strong threat by moving the Knight? Indeed, he can. He captures the K.P with the Knight, thus attacking the Bishop with his Queen. And if BxQ, the threat of White against the King is executed: BxPch., K-K2; X-Q5 Checkmate. This motive recurs often. In an opera called the "Seekadett" ("The Cadet at Sea") a short game of Chess is played on the stage and it is this motive that is used on that occasion.