Keeled scales

[2] Non-European lizards such as Sphaerodactylus macrolepis also display keeled scales.

He then references a 1938 study, stating that it "has suggested that the keels may have an adaptive advantage in reducing shininess, that otherwise might lead to discovery by enemies.

"[4] The purposes of keeled scales are largely understudied, but some other uses may include locomotion in arboreal and grass-dwelling species.

The snakes use this in a warning and threat display: the body is arranged into a series of parallel C-shaped (counterlooped) coils that they rub together continuously to produce a sizzling sound, rather like water on a hot plate.

[7] The sprightly little sphaerodactyl: Systematics and biogeography of the Puerto Rican dwarf geckos Sphaerodactylus (Gekkota, Sphaerodactylidae)