...A planarian worm, which has long been studied for its regenerative properties, is able to grow back a lot more than just its body parts: after the worm's small, snake-like head and neck are removed, its body will even regrow a brain that's capable of quickly relearning its lost skills. The researchers tested the memory of planarians by measuring how long it took for them to reach food in a controlled setting. The small worms dislike open spaces and bright lights — but they had been trained to ignore it so that they could find their meals. Even after decapitation, worms that had gone through training were able to overcome their fears and start eating much faster than worms that hadn't been trained. However, the memories didn't come back immediately. Each worm still had to be reminded of its earlier knowledge, though it only took a single lesson for it to all come back.