Sea snakes are widespread and conspicuous inhabitants of shallow waters in the Indian and Pacific Oceans. They are agile top predators and possess extremely potent venom, but they are still susceptible to predation by large fish, e.g. sharks, and other vertebrates. We describe how crevice-probing and temporarily non-vigilant Yellow-lipped Sea Kraits Laticauda colubrina twist the tail around their length axis so that the tail tip's lateral aspect corresponds to the dorsal view of the head. In doing so, coloration and pattern in combination with tail movement and posture make the tail appear very similar to the (non-visible and foraging) head. We examined 98 Laticauda spp. sea snakes in three major museum collections and reviewed the literature to assess the generality and implications of our field observations. This leads us to hypothesize that a combination of: (i) head and tail being similarly coloured and patterned, and (ii) the tail being motioned to resemble the head, is a hitherto overlooked mimetic and 'prophylactic' anti-predator adaptation in the L. colubrina complex, and possibly in other species of sea snake. We propose this is a concerted behavioural–morphological adaptation, and we briefly speculate about its possible fitness trade-offs as well as its origin. Explicit and testable predictions derived from the hypothesis are presented.