Q:  How can one tell whether one is in the presence of another cannibal?
A:   Generally, they have incisive reasoning and big strong teeth, the better to masticate with, even stronger incisors, a sharp wit, and a very sharp knife.  They like to check out their prey a bit with some firm squeezing, a little mild pinching to test the tone and firmness of muscle and fat.  They also have a lean and hungry look about them and cannot maintain their eagerness to sample a tid-bit so always stand clear or you will get bit.  Once bitten, it's on.