The display is a bluff by a lizard with no venom, modest speed and limited biting power. Cornered, it flattens the body, hisses, opens the mouth wide and protrudes the tongue.
Measurements published in 2018 by Arnaud Badiane and colleagues found that the tongue is not uniformly coloured: the posterior region reflects roughly twice as much UV as the tip, and is about 40 percent more luminous. Presenting simulated predators to skinks showed that full tongue protrusion, which exposes the bright rear surface, came late in the sequence, once the threat was close. That timing fits a deimatic display, meant to startle a predator at the point of attack rather than to warn it off from a distance.
Many of the skink's likely predators, including birds and snakes, have UV-sensitive vision, so the signal is probably more conspicuous to them than to a human observer. What the display is honestly signalling remains open, since the animal is not toxic; startle alone may be enough.