This is not a donkey. This is a mule. It bugs me when city folks get them mixed up. Donkeys and mules have entirely different looks and personalities. A mule is probably almost as smart as most men, and smarter than some. It is totally a donkey.
Baby racoons will do this when they are happy and feel like they are protected and safe. I've had several litters of baby racoons and they would always purr when they were curled up in a warm spot, nursing or when we'd pet them.