A couple of my snakes required blood to be on the pinky when I was switching them over. All of them are different, so if the slime doesn't work, I'd try a bit of worm blood slathered over the pinky.

And, Dae is right (at least this is true for all of my snakes), they like colder food. My mom, when she helps me feed, takes a pinky and puts it in hot water and thinks they want it warm, but none of them will take it. If it's cool, they happily take it.