Well they pick up vibrations awful fast!
It is NOT the water from the spray bottle causing my Ball to recoil. He is on the other side of the cage. And, it is Immediate!
Also, he moves just as I open the door, which makes a fairly loud sound- even though from a distance.
If the door is already open I can walk right up to cage at times and he is undisturbed- until I speak to him.
They may not have auditory nerves, but they "hear" via vibrations through their tummys on the ground and their pits and other bone structures in their skulls.
Just how deaf folks can hear/feel vibrations through their mastoid bones in the skull and feel vibes with feet and body.