Sometimes the ball python teeth are so fragile that tiny tiny pieces break off into your skin. Maybe if you didnt thoroughly clean it last week, the teeth might still be in your skin? Otherwise I've got no clue.
Snakes have an anti-coagulant in their bite, and it makes you bleed a bit more than a normal cut or bite. Since you bleed more, it gets rid of all the bacteria and fresh blood then sets on top to scab. This makes it a bit hard for snake bites to become infected, in case you were wondering.