if you count the hand out you know partner has a max of one jack
and you are holding two of those so partner has nothing the dia j
or the spade J (and declarer is making an unusual play in spades).
Given this info you can see declarer is due 3h 4c 3d and (unless making
a weird play in spades) 2s. Declarer is always going to make this hand so
the only question is what is the best way to defend. Well oddly enough
since opener must have the heart AKQ and you can see 4 hearts in dummy
you know you will be squeezed out of your spade K on the run of the minors
anyway (or your 4th heart) sooooooooooooooooooooooooooooooooooooooooooooooo
you might as well cover the spade Q and hope p can cover the suit from there.
By coincidence covering the spade Q also works if declarer is making a weird
play in the spade suit so its at worst a no lose shot (naturally this will be
the hand where opener opened a 19 count and ducking would have been best:)