Chess in 40 SecondsThe Kieninger Trap
Black to move. Mate in 1.
Snort just grabbed your bishop on b4. Mate him.
Hint
His e2 pawn can't take anything — moving it would expose his king.
Answer
Nd3# — Checkmate! The king is stuck behind its own queen and pawns.
The idea
A knight check can't be blocked. A king stuck behind its own pieces has no escape.
This chess trap is one of 30 quick puzzles in the Chess in 40 Seconds trainer: find the move on the board, get a hint if you're stuck, and learn the idea so you never fall for it in your own games.