i think they can judge distances pretty well. most of the time you can tell by how they position their bodies that they are about to jump and you can either put your hand in front of them, or if they are going to jump on another person they can step closer if need be. when i have eenie out by myself i will sit on a chair and make kind of a small space for her to be inbetween me and the aquarium. that seems to work really well, rather than just walking out into open space with her where she could jump out into nothing if she got startled. this way she can either jump on the outside of the aquarium, onto me or stay on the table space inbetween.