Fear of heights

Source: news.sciencemag.org
We don't really know if snakes are afraid of heights, but we are certain that they hang on very tightly when they climb trees. Research has demonstrated that snakes exert up to five times the effort required to keep them from falling.
Ten snakes from five different species were tested in a lab experiment. First, investigators outfitted a flat surface with sensors and covered it with fabric. As the snakes moved over the surface, the sensors measured the force the animals exerted for their forward movement. Next, the experiment was run with the same sensors and material on a vertical pole 2.4 metres high. All of the snakes climbed the pole with a ‘concertina’ movement: each snake clamped one part of its body around the pole while pushing or pulling other body parts upward. On average, the snakes used three times the force necessary to climb the pole and counteract gravity.

Clearly, the snakes’ built-in safety factor – up to five times the force required – costs them energy. The investigators explain this in their Biology Letters article: the effort also yields an evolutionary benefit, as a fall from a tree has grave consequences.