As south, I reached a poor slam with at least two certain losers. A spade was led away from the KJ, giving me a spade trick I wasn't entitled to. I won the queen and crossed over to the ace of spades. I led a trump to the ace, and west dropped the jack(!) letting me get away with no trump tricks. The rest is simple.
The problems here are
-West playing the Jack of trumps
-A risky lead (?)
Although the lead doesn't matter because I can discard my spade on the final club, it was still potentially disasterous.