the swelling is norm if it was a mouse or rat.. it happens to me and my wife when a rat bites us.. but it never gets infected.. just a lil red and then turns a bruise color.. i do believe a rat bite is more of a pressure puncture than anything .. but i would wait for someone else to post in here.. but imo your snake will be fine .. next time u should break its back before feeding or kill it urself .... a small book across the neck works just fine.. quick and painless.. unless you dont break the neck all the way.. then it lays there and just breathes lol ...
dont know how to tell if it is infected on a snake.. but im sure it wouldnt be asap more like over a few days