Three characters settle the identification without ambiguity. Snakes have no movable eyelids, their eyes covered by a fixed transparent brille; glass lizards blink. Snakes have no external ear openings; glass lizards have a visible opening behind each eye. Snakes have loosely connected jaw elements allowing enormous gape; the glass lizard's lower jaw is fused at the front, restricting it to prey it can fit in an ordinary mouth. A deep lateral groove down each flank, absent in snakes, allows the rigid, scale-armoured body to expand after feeding and during egg development.
The name refers to caudal autotomy. The tail, which makes up roughly two thirds of total length, breaks along preformed fracture planes and thrashes while the animal escapes. The regrown tail is shorter and differently scaled, and the animal cannot repeat the trick indefinitely.
The old folklore that a broken glass lizard reassembles itself is untrue. Limb loss has arisen independently many times in squamates, in glass lizards, skinks, pygopods and others, so the resemblance to snakes is convergence rather than kinship.