My friend's son behaves exactly like this and has an ADHD diagnosis along with some other significant behavioral issues. He has a severe lack of impulse control and the majority of it revolves around food/putting things in his mouth, makes me wonder if that's what's happening here. Will never forget the time we all lived together and as I was bringing friend's son in through the garage after school dude bullldozes past me and throws himself to the ground to lick a puddle of oil that was leaking out from our mower. Wild stuff.