Perhaps it's because we are now a pet-free home or maybe due to the fact that Zachary crawls around like an animal, but apparently Matthew now thinks of his baby brother as some sort of mammal other than human. He has taken to patting Zachary on the head (I'm surprised it's not accompanied with "good doggy"), occasionally tries to ride Zach like a horse (thankfully baby ZJ is one tough little tyke), and most recently has begun setting up obstacle courses for Zach to clamber over and through. Zach definitely would win 'Best in Show', as he crawls over packages of diapers, successfully plows over Kleenex boxes, and climbs into laundry baskets with the agility of a miniature poodle, yet leaving a wake of destruction comparable only to that of a robust Rottweiler.
Oh, and he drools too. Maybe that's where Matthew gets the connection.