unusual animal friendships - dog and frog

a rhyming friendship! full details at http://www.cuteoverload.com

unusual animal friendships: lambs, rottweiler

Another animal friendship reported by the BBC here.
I guess there should be categories - sibling friendship, adoptive parency, playmates, etc, with additional labels, like "would normally kill/eat each other", "not native to same environments", "size differential".
This would help us work out why they're unusual and work towards our ultimate goal of creating better animal friendships.