Yinrih have a caudal ganglion, which is a secondary brain located at the base of the tail whose original purpose was to control the tail, but which has evolved secondary functions as a sort of backup for the main brain. Yinrih can withstand head injuries that would render a human dead with no long term consequences as the main brain can rebuild itself from information stored in the caudal ganglion–a very useful feature if you fall on your noggin from a tree on a regular basis.
There's a neurological disorder caused by a partial severing of the connection between the two brains where the tail acts on its own accord.