So East is on lead in 3NT on the given hand (FWIW, the contract is 3NT and East is cashing the 4th defensive trick but...). He/she cashes the ♣9, and their partner has to discard a ♦ winner. If they keep it, they have to unguard ♥/♠ and then declarer can get out for -1...By discarding the ♦Q, East can play a ♠ for -2.
What squeeze is this? Thought it was quite a nice ending.