Why has my snake swelled after eating?

I agree with the other people who are saying your snake is still digesting it is .But i have never seen a boa (red tail) or any other snake expand to 4 times it normal size after eating .It could be that the rat you gave was far to big or it may have a gas build up(very unlikely).The best thing you can do is wait one more day then call a vet and ask advice if the snake is still bloated or as the others say it might just be digesting