The microscopic flatworm (Stenostomum brevipharyngium) is one of nature’s weirder creatures. Chop off its head, and it’ll grow one back. Cut it in half, and it’ll become two separate healthy worms. And now scientists have discovered an even stranger trick. These unsegmented, soft-bodied invertebrates can grow two heads, a normal one and a backward-facing one, in the middle of their bodies where their tail should be. This developmental error lets the worms permanently reverse their head-to-tail body axis without any noticeable harmful effects.