don't give it gerbils, some snakes become "stuck" on gerbils, so unless you want to be spending 6 bucks everytime the snake wants to eat, and getting about 4 gerbils everytime he has to eat, it will get EXPENSIVE.
Try a small(very small) rat, firt f/t try heating up some water in the microwave (without rat) for about 6 minutes, then put the rat in a baggie, and put the baggie in the water, take a spoon or something and hold it down under the water.
if you squeeze it slightly you should feel NO coldness, infact it should feel quite hot to you.
now take the bag out of the water and take it to the snakes cage, use tongs, and get the rat out of the cage, by this time the rat should be cooled enough that it won't burn the snake while eating it (if it eats).
wiggle the rat a little to the left or right of the snake, not the front (heat pits are to the sides a little). Don't touch the snake, as this startles some snakes and they will just ball up.
If that don't work try dipping the rats head in the still (should be) steaming water for a few seconds, then, dripping wet, let the water drip near the snake, this always works for my picky female.
f/t tricks
braining (take a tack, or needle and open the skull up a bit)
cut the nose off
let thaw out in mouse bedding
put in a paper bag with f/t item over night (put paper bag in original enclosure just in case of an escape)
if house on news paper or paper towel leave f/t item infront of hide that the snake is in.
leave a live rat pup in overnight (make sure it does not have it's eyes open, something a little under 2 wks old) they wiggle around alot more than pinks/fuzzies, and about the size of a SMALL mouse.
and as someone already asked, what is the cage like
how are you providing heat
what are the temps
how are you measuring temps
whats the humidity
whats the size of the cage-snake
how many hides
does he have a water bowl big enough to soak in
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1.1 Ball Python, 0.1 motley amel corn, 1.0 western hognose, 1.0 red blood