The aye-aye is one of the ugliest and strangest of primates. A nocturnal lemur, it has a curious adaptation in the form of an elongated middle finger which is perfect for holding on to a coffee cup - No, wait. There are no paper coffee cups in the wild in Madagascar, so although that fellow at the Duke Lemur Center has found a civilized use for his unique digit, that can't be right, can it?
Right. In fact, what the aye-aye does is use its finger to tap on trees to find cavities within them that might contain tasty grubs. It uses its teeth to dig into the cavity, and then the long finger fishes out the food.
The finger is extremely sensitive to vibrations, and now some scientists have discovered that it has another unusual property. When the aye-aye is searching for food, the finger heats up by several degrees, but is much cooler at other times. In the thermal image, you can see that the finger is black - cooler than the rest of the animal - when it's not in use:
It remains to be determined exactly what the mechanism is for heating and cooling the finger, but as for reason, the researcher says "Like any delicate instrument, it is probably best deactivated when not in use."