Symptoms of gangrene look like what?

Gangrene: In the early stages, gangrene typically begins with a wound surrounded by redness followed by tissue death with darkened avascular tissue, drainage, air entrapped in the tissues causing a crunching sound with eventual malodorous drainage and red streaks running up the leg followed by fever, sepsis and eventually death may occur in untreated gangrene.

Dark tissue: The tissues that become gangrenous are dead because they have lost their blood supply. Eventually they become a shade of grey or black.