Snakes move their scales to increase friction

Snakes can climb a range of surfaces, from tree trunks to brick walls, using a hitherto poorly understood mechanism. The bellies of snakes are covered in a series of flexible scales that can be activated by the snake to prevent sliding. It is previously shown that conscious snakes can use this ability to double their friction coefficient relative to unconscious snakes. In this combined experimental and theoretical study, we give further evidence that snakes actuate their belly scales. We perform experiments where we slide snakes backwards atop an array of pillars. Our theoretical model suggests that snakes that do not apply an opening moment to their scales should have quite short contact with these pillars. In our experiments, snakes slide their ventral scales down the pillars, prolonging contact. Our modeling suggests that this phenomenon can only occur if snakes apply a moment at the scale base. We hope this result encourages further research in actively-generated friction.