Okay first off why are you wanting to feed it live prey? If it's eating f/t perfectly fine, I would keep it on f/t. As pinkies and such there should be no problem with the mouse attacking back, but as they grow you could wind up with the prey attacking the snake before you can even do anything about it. AND YOU HAVE TO STAY BY THE CAGE NO MATTER WHAT. Don't make me post the picture about the irresponsible $#$#@%#^@$# that left that live rat in with his ball python for god only knows how long and the damn rat ate the snake... This IS due to owner messups but you have to MAKE SURE you are not that type of owner. I know people who have kept a rat in the same tank with a snake for over a month. I saw it, whacked its head and the snake ate it right up. You can't leave live prey in with your snake for extended periods of time. And you have to be ready to pay for the vet bills. As I said, they can attack before you can get to them. Even a scratch or something from a rat claw can wind you a $200 trip to the vet. It's eating f/t, keep it on f/t if you want my opinion.
But the reason he's not constricting is because its not a threat to him. When they get larger he will constrict, rather it be a f/t or live. I have a black rat snake that eats f/t and has constricted everything since he was on pinkies. If you are just obsessed with seeing it squeeze, wait til it grows some then feed it with a pair of tongs. Hang the thawed mouse by its tail and your snake will attack as if it was alive.
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Chondros and colubrids... my 2 favorite types of snakes!
"Life is hard. Life is harder if you're stupid." - John Wayne