I thought it was *flag*

Where does the saying 'like a red rag to a bull' come from?

The color red is supposed to enrage bulls. Actually it's probably the waving of the rag that attracts the bull's attention. I believe a bull is suppose to be color blind. Anyone know?

I heard that too. The capes that matadors use in bullfighting are red and that's where the phrase comes from.

Bulls are certainly colour blind - which can be seen from the structure of their eyes, it is not merely a guess. It is the flapping movement which would attract a bull's attention (though in bull fighting, having had the 'pics' stuck into its shoulders first probably don't improve its temper very much either!)

I thought it was "like a red *flag* to a bull". I'd never heard the word "rag" used in this phrase.