The boop, or 'zerbert,' is an expression of affection that goes back to caveman days. I know this, because I was there. Neanderthal women would cuddle up to their dirty, stinky babies and apply their lips to a soft cheek or belly and go "PBBBBBBTTTTBBBPPPPPT!" to the giggles and wiggles of a now happy baby.
It's a known fact animals like affection too. Plus, they're furry. And who doesn't like fur? Nobody, that's who. So, pick up the next animal you see and give it a healthy boop on the tummy or neck or wherever it doesn't have claws or teeth or matted clumps of whatever it just rolled in.
Bonus points if it's not your animal.