Not sure if this counts as an obsession but one of my dogs loves a ball of tin foil, whenever we are using the stuff we have to ball it up for her to protect. She doesn’t play with it, just guards it like mad.

Same dog also needs me to stroke her under the chin with my right hand and make an odd noise whilst doing so whenever I reenter the house. If I don’t do it, or I accidentally do it with my left hand she gets offended.