They pick up on movement. It's also true of my retics - sometimes they will strike a feeder so hard it gets knocked off the tongs. Now, I am not reaching into the enclosure, even with tongs, to try to grab the feeder and offer it again; I just close the door and let the snake find it. Sometimes it takes them a while; I've even had a few use it as a pillow or crawl over it before realizing that it's food.