List all of the legal actions that Alice can perform.
What action should Alice perform?
Bob has a yellow 2 on chop, which would normally need to be saved. However, Cathy already has the other copy clued in her hand, so Bob's yellow 2 is trash and should be ignored.
Bob also has two 5's, but neither of them are on chop, so they cannot be saved yet.
Cathy has two 5's. One of them is already saved (i.e. has a clue on it), but one of them is not already saved and is on chop.
(Cathy's chop is slot 2 because the cards on slot 3 and slot 4 have a clue on them.)
Thus, the actions that Alice can perform are:
to save Cathy's 5
to discard
But which is better? In this situation, either Alice or Bob can save the 5:
If Alice saves Cathy's 5, then Bob would discard a yellow 2 (which is trash).
If Alice discards, then she would discard an unknown card, and Bob would save Cathy's 5.
Since discarding trash is better than discarding an unknown card, Alice should give the clue to let Bob discard.