This creature can disguise itself as a branch
Remember how we said that some animals were masters at camouflage? Some bugs are, too, like this eight-legged arachnid. It did not care that it was not on a tree. Nothing could keep it from fulfilling its evolutionary purpose.
Of course, its purpose was disguising itself as a branch. Admittedly, it did not quite succeed in blending in with its surroundings. Still, any passer-by could easily assume there was a branch stuck to the curtain.