I've had my snakes "zone in on" my hand when I didn't have the prey warm enough. They like it really warm! Are you offering with tongs? That makes a difference, too. The tongs will be cold so they won't focus on the tongs, just the food. I always feed my snakes in their cages and I have had 0 cage aggression over here. I'm sure it's fine to feed in a separate enclosure, but to do so for cage aggression is a rumor when it comes to ball pythons.