A red 2 on slot 4 clued with a number 2 clue. (Bob does not know the identity.)
Alice clues number 3 to Cathy, touching a 3 on slot 3 as a Play Clue.
Bob plays the red 2.
Which notes should Cathy write on her 3?
What should Cathy do next?
Cathy's 3 might be a red 3, which would make Alice's clue a Prompt on the red 2.
Cathy's 3 might also be a blue 3, which would make Alice's clue a Hidden Finesse on the blue 2.
Since both clues are legal, Cathy writes r3, b3 if b2 f on her card.
Thus, Cathy cannot play her 3 right now, so she must discard or perform some unrelated clue. Notably, Cathy should not clue the blue 2, because that might Stomp on the Hidden Finesse.