Basically you have 3 choices.
1. offer and it will eat it
2. offer and it will constrict it, kill it and slither off to a corner to chill with the first one in it's belly.
3. it will slither off to the corner and ignore your attempt to feed it.
I feed multiple small prey items all the time and have no issues.
Maybe the small rat is too big and a weanling size rat would be more appropriate?