To become extremely angry or enraged, often to the point where rational thinking is impaired. The phrase implies an intense, overwhelming fury.
This expression comes from the ancient belief that extreme anger could literally affect one's vision, making everything appear red-tinged. It may also relate to the association of red with blood, danger, and aggression across many cultures, or to the reddening of the face during anger.
Interestingly, there's some scientific basis to this phrase - extreme anger can actually affect peripheral vision and color perception due to the rush of adrenaline and changes in blood pressure. Bulls don't actually see red (they're colorblind to it), but humans experiencing rage sometimes report visual distortions that make this metaphor surprisingly literal.
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