Blood conveniently is an intense red and it can spread over a large area without losing much of its color. A nosebleed, for example, can look quite dramatic.

Pain also is highly subjective, and can depend on psychological factors. A gladiator may have thought “that looks as if I fought hard, so they will let me live, and it is survivable”, rather than “that’s half an inch deep, bleeds like , and I will never be able to use that arm again!”

Regardless, that gash in your fat arm easily beats an equally sized gash hitting a major artery or cutting into a bone.

It's just a flesh wound!