A burn is caused by exposure to too much heat. Belly rot is caused by an exposure to too much moisture.
Typically belly rot will look like the edges of the belly scales are rusty. If you are concerned about either of these, I'd really suggest a trip to a vet so you get the necessary medications to treat it.
Cause when push comes to shove you taste what you're made of
You might bend, till you break cause its all you can take
On your knees you look up decide you've had enough
You get mad you get strong wipe your hands shake it off
Then you Stand