hat that cardinals and pope wears.

[Minnesota]

The little round hat that the pope and cardinals wear looks like the jewish hats. Why is that?

[Clanad]

Called a zuchetto, it has no connection with the yarmulke, worn by some Jews.  Tradition suggests it was developed to cover the tonsure, the shaved central part of the skull favored in the middle ages by priests of the Catholic faith...

[Minnesota]

Huh.......who knew! Thanks for the answer.

Clearly, I am not Catholic or Jewish! But love to learn more!

[WaldoMcFroog]

My original answer was going to be 'Because Jewish hats are small and round too...' ;-)

But to add to Clanad's answer, the tonsure is itself thought by many to be symbolic of trepanning.

Trepanning is where a small bore hole is made in the skull. The belief was that it relieved pressure on the brain and also brought the trepannee closer to God. Modern adherants of treppaning say it gives a mild euphoria, similar to the early stages of an LSD trip.

I once read of a man who attempted self-trepanation (if that's even a word) with a power drill. Halfway through, there was a powercut.

He was one of the druggie types, not a religious type. Probably didn't need to add that.

[jno]

The tonsure was one of the big causes of dissent between the early Roman and Celtic churches (the dating of Easter was the other one). Roman tonsure was as mentioned above. Celtic tonsure involved shaving the whole front half of the skull. Amazing the things that bishops get worked up about.