Word to the Wise: if you suspect those around you of being snake-people disguised as human beings, chant this little ditty--Ka Nama Ka Lajerama.
After a few minutes they should shed their false skins to reveal themselves as the wretched, reptile-headed mutants they are. OR...they'll just look at you as though you're crazy--in which case they are NOT snake people, and you should not slay them.
Now you know. And knowing's half the battle, G.I. Joe.