Is there any chance he smelled other animals (like prey) on you? I've kept MBK's in the past & never had a problem with them doing this, but I've also kept other kinds of king snakes (California kings etc) & first off, most king snakes are "always ready to eat" & 2nd, some are more "open-minded" than others about what is edible. In the wild, many king snakes will also eat carrion & I had an albino Cal-king that once tried to eat her own tail when she was quite old...I don't know if she was getting senile or what? And she was well-fed, too.
How old is your MBK? or how big? How long have you had? Any chance he's under-fed? MBK's are probably my favorite kind of king snake- they seemed less prone to stuff like this.
Was he ever fed live rodents (especially from questionable sources) that might have given him parasites? If so, he might have good reason to be hungry (& might need de-wormed).
Sometimes a snake that's confusing you with "dinner" can be dissuaded by making sure you smell of something less appetizing (also that's harmless to the snake). Might try rubbing some minty mouthwash on your hands & arms- or wash your hands & arms thoroughly with a fragrant soap before handling. If you haven't been handling him much, you might need to "socialize" more often with him so he really knows you & knows you aren't his dinner...silly snake!
I've seen a rosy boa do this same thing to a friend of mine, during a snake lecture we were giving jointly- it wasn't his snake though, it belonged to the nature museum. Anyway, my friend saw what the snake was about to do (the rosy boa kept pushing slightly here & there on his hand, testing & "looking for the head to grab", lol) but my friend just ignored it & let the snake bite him so he could show our audience just how big of a deal this bite WASN'T. The tiny teeth marks were nothing to my friend anyway- he was diabetic & had to inject himself all the time.![]()
I'm not sure what you're getting at regarding the "damp spot"? He might have drank water & spit some out when you picked him up?![]()