This is definitely one of those super sweet, charming videos that I particularly like because it is interspecies companionship. This appears to have happened spontaneously and instantly when a little kitten meets up with a deer in a bath who I presume is recovering from an injury to her leg and is being cared for by the lady who lives in the house.
If this is a first encounter, it is amazing that the deer immediately sets about washing the kitten as if the kitten is one of her offspring. Initially the kitten is not too sure about it but then at the end of the video you can see that she begins to enjoy it and accept it completely — the bond has been created. Beautiful.