No one knows exactly when the aggressive arching
of
an angry cat's back suggested these words for humans aroused into anger,
but it's surprising that the phrase to get one's back up is not more than
two centuries old, for an angry cat with its back arched high when
attacked by a dog or other animal is an impressive sight and a common one
wherever there are felines wild or domestic. Cats were introduced to
Europe long before the Crusades and became valued pets, despite their
aloofness, when they demonstrated a proficiency at rat killing at least
equal to the ferret's and proved far more prolific and easier to keep.