With none vul at IMPs, you see the following.
Partner leads the ♥A and all follow. Now partner plays the ♣2 and dummy plays the 3.
You have to finesse against the ♣6 to have a chance to beat this. Now, when declarer leads a low spade from hand at trick 3, partner has to NOT play his ♠K so you can win and draw the other trump, since declarer has ♠AJ85 ♥6 ♦void ♣AKQJ9875. Of course, partner knows you can beat the ♠10 since if declarer had ♠AQJx they would lead a quack to guarantee the contract.
It only happened this way in my dreams. In real life, my teammate led the ♦Q against 5♣ and declarer got a heart pitch and spade ruff to make game, while at my table we chose the rather unsporting contract of 3NT by N and after a heart lead and diamond switch partner claimed 11 tricks.
Plus... it's free!