The correct way to bind a rat's mouth:
First, make an appointment with a qualified surgeon, preferably one with battlefront wartime experience. They work better under pressure.
Take the rat that is going to be fed off to the hospital. Now, here's the tricky part - getting past the red-tape so you ONLY pay for the actual surgery to hold the mouth shut, and NOT pay for any anesthesia or ancillaries.
Pay the book keeper under the table - a $50 bill should do the trick, and have him/her ONLY submit the claim for the surgeon and the time for the O.R.
After recovery, you should have a rat with a nice, clean sutured mouth - ready to feed with no harm to your snake. And it only cost you $2500!
THAT, my friend, is a BARGAIN!