Deep in Madagascar's rainforest, a creature taps bark up to eight times a second with an impossibly long, skeletal middle finger. With rodent-like teeth, a bushy tail, and huge staring eyes, the aye-aye baffled early scientists and terrified local cultures alike.

This episode reveals how every "monstrous" trait of the world's largest nocturnal primate is actually a finely engineered survival tool. We follow its tangled taxonomy, its woodpecker-like ecological niche, its strange social life, and the deadly superstitions that nearly drove it extinct, making the case that the aye-aye is a masterpiece of evolution we simply failed to understand.

• Why naturalists kept misclassifying it as a rodent before the petrosal bullae revealed it was a lemur
• Percussive foraging and ears that work like an acoustic Fresnel lens to locate gr ...