But how do animals know their “ups” and “downs”?
You are fortunate (and so am I of course) that we have no problem to detect what is up and what is down. We, and most other vertebrates, have gravity receptors, sense organs in the inner ear, which consist of a cushion of sensory hairs with small crystals of calcium carbonate and calcium phosphate as weights spread across them. Depending on whether vertical acceleration of the vertebrate animals is towards or away from Earth, this earstone material either de- or increases excitation of the sensory hairs it rests on; thus, creating the sensations of rising and falling and an awareness of being lifted or dropped. —>—>