Brilliant syllogism

A scientist worked for years trying to teach a cockroach to respond to verbal commands. Eventually he succeeded in getting it to leap over his finger whenever he told it to jump.
Once it had learned this, he pulled off its front legs.
When he then commanded the cockroach to jump again, it took a deep breath and just managed to clear the man's finger.
He then pulled off the middle legs and on the command to jump it just managed to stagger over.
Finally he pulled off the back legs.
But when told to jump, the cockroach just lay there, legless.

Conclusion: when all a cockroach’s legs are removed, deafness occurs.