I have my son's BP in a tank, and when it is out and following my every movement, I know it's hungry. Come to think of it, it seems to be hungry all the time anymore and I bumped it up from weanling rats to small rats to boot! May need to bump it up again. My own BPs are in racks and since I feed every Tuesday, I look for them being very alert with tongue flicking when I pull out the tub.