Is It Possible to Revoke During a Claim?

On today's deal from the Friday duplicate, all four players were culpable:

The bidding was typical: south preempted with an inappropriate hand, and north took a wild gamble.

The opening lead of the spade king fetched the seven and six.  West should have considered more carefully that declarer might have attempted a falsecard in the suit, but in fact that would have backfired.  A falsecard here has a chance to work only if all of declarer's spades are higher than east's play.

In any case, west continued with the ace of spades, ruffed.  Two top hearts followed, then a diamond to the queen and ace.  Declarer now led a club to dummy and claimed — but the story doesn't end here.

East, somehow aware that he was still in possession of a trump, contested.  Displaying the heart jack, he stated that north's second club would win but that he would ruff the third, leaving declarer with a diamond loser.

South promptly acquiesced, apologizing to partner for not having drawn all the trumps.  The hands were folded up, a score of -50 was entered on the traveler, and the foursome proceeded to the next board.

Anything can, and does, happen at Dante's Infernal.