Alice clues blue to Bob, touching slot 3, slot 4, and slot 5.
What slot is focused?
Is this a Play Clue or a Save Clue?
What card note does Bob write on the focused card?
Slot 4 is focused (i.e. the "new" card that was on chop).
Blue 1 is played on the stacks and Bob already has a blue 2. Thus, the focused blue card can be either a blue 3, a blue 4, or a blue 5.
If it is a blue 3, then this would be a Chop-Focus Delayed Play Clue through his own blue 2. That is legal.
If it is a blue 4, then this would be a Critical Save on the blue 4.
If it is a blue 5, then it wouldn't make any sense, because blue 5 is not playable. Blue 5 is critical, but it must be saved with a number 5 clue as a 5 Save.
Thus, this can either be a Chop-Focus Delayed Play Clue on the blue 3 or a Critical Save on the blue 4.
Bob writes a card note of "blue 3, blue 4" on his slot 4 card.
Note that before this clue, Bob was not able to play the 2 in his hand, because it could have been the yellow 2 (which is not playable).
This blue clue "filled in" his 2 to be the blue 2, so now Bob can go ahead and play it.
However, this does not make the clue a Play Clue. Since it was focused on slot 4, it is first and foremost a potential Save Clue that happened to have a "side-effect" of making the blue 2 playable. (Blue 2 was not the focus of the clue.)