I did end up researching Pavlov after posting and whether he had any famous paradoxical discoveries. This joke was copypasta from a submission site I am afraid, lol. They are doctors, a pair of docs.

Some of the cats might be dead due to Shrodinger’s paradox.

They are doctors who have paradoxical theories (pair of docs) but after some research Pavlov’s theory of conditioning is not a paradox so the site I ripped this joke off of may have used the wrong doctor.

It both makes sense and doesn’t at the same time but eventually the punchline might ring a bell.

Getting this joke takes joint effort.

No, the flies know what they’re doing.