At the table yesterday on Common Game deal four I thought my opponent had done something bizarre...but in retrospect I wonder.
Unopposed you bid 1♥-2♣-2♥-3♥. 2/1 and 3♥ promises at least some slam interest.
You choose to bid 5♦ exclusion Keycard, and get a response of 5♥ -- your partnership foolishly plays that as one keycard.
6♥ of course and this dummy goes down.
No you don't bid 6♥; you bid 5♠ asking for the trump queen, knowing you wont find it and can sign off in 6♥.
Why does that matter -- well ask yourself what you would lead with eg
Wouldn't you 'know' no ace was missing and lead a spade to try to set a trick in suit up before it went on the clubs?
As it happened partner dummy was about to put down Kxxxx of clubs and a singleton spade, so the only way to beat the slam was a club ruff...but alas the hand on lead (my partner) had A10xx and gave me the ruff.
Plus... it's free!