Snot, vomit , excrement, spit , semen : physical monsters vs moral monsters

We've all seen enough films and TV to be wrongly confident of what a typical lifelong serial contract killer looks like.

They are ultra normal looking .

Even good looking.

Oh so symmetrical in features and body shape, modest in speech, polite, neat , always tipping the waitress well, always picking up a fluffy animal 'for the daughter' on these infrequent way-from-home business trips.

But their quick, clean, cold hits include a lady doctor who advises on abortions, an investigative journalist and a small time drug dealer who ran short on his returns to his supplier, Mr Big.

They are , in a word, a moral monster : with our fascination for them entirely wrapped around how such seemingly normal people can be so evil.

Now physical monsters are not merely scaled up ten feet tall versions of Ms Right, the serial killer, a monster who can now kill with her bare hands instead of with a high powered sniper rifle.

Instead these monsters are always disgusting and repulsive , as well as being cold blooded determined to kill on sight.

Why ?