Try a live mouse hopper.
I wait a month after the first shed before attempting an assist feed.
And there are a few assist feeding vids on youtube you can look at for reference. When I assist feed, I use p/k rat pinks.
I hold the snake gently and grip my thumb and index finger behind its jaws. I maneuver the rat in front of the snake and use its nose to wedge open the snake's mouth. I push the rat until its nose is in the back of the snakes throat and push his mouth close. The snake's natural feeding response usually kicks in around here. Some may fight you and spit the feeder out.
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