It's a caterpillar.
Hemeroplanes is a genus of moth, with species living from Mexico to South America. Its caterpillars have evolved a way of frightening off would-be predators: look like a viper, and attack them back.
Unlike the many caterpillars with a false head on the tail-end, Hemeroplanes' snake-head is also its real head. It's also usually invisible, as the caterpillar normally looks like a totally normal caterpillar.
(Notice the green belly.)
But when threatened, the caterpillar detaches all but its back legs from the branch. Its green underbelly now exposed, it pulls its head into its body, which puffs out the body at the tip. As its skin folds and wrinkles like a living origami project, formerly diffuse specks of color rapidly coalesce into the image of a deadly arboreal viper.
To further sell the lies it's peddling, the caterpillar will go so far as to lash out at would-be predators, simulating the sinuous strikes of a venomous snake.
Oddity Central had a nice write-up of these natural-born liars a few days ago. And Gianfranco Gómez has quite a few photos of the transformation in-progress (which apparently only takes a few seconds).