Answer: CS (Conditioned stimulus )
Explanation: Conditioned stimulus is the formerly neutral stimulus that generates a conditioned response after getting in contact with unconditioned stimulus.
As per the situation described in question, can opener's sound is acting as the conditioned stimulus because earlier the can opener was neutral but after coming in contact of can(unconditioned stimulus) for getting opened , it creates whirs sound that is the conditioned response which attract the cat(Fluffkins)