Most octopuses hide by matching the background or squeezing into a crevice. The mimic octopus lives on featureless estuarine sand flats where neither option works well, and instead changes its shape and movement. Flattening its arms and undulating along the bottom produces a flatfish-like swimming form. Holding six arms in a burrow while extending two banded arms in opposite directions resembles a banded sea snake.
The field observations that founded the description, by Mark Norman and colleagues, recorded these postures repeatedly and noted the sea-snake posture appearing when the octopus was harassed by damselfish, which sea snakes prey on. That context-dependence is what separates the case from an octopus simply being an odd shape.
Caution is warranted about the longer lists that circulate. Popular accounts credit the species with fifteen or more impersonations; the peer-reviewed record supports a much smaller set. Whether the octopus is deliberately targeting a specific model, or producing a generic threatening display that observers interpret as particular species, is not settled.