Poor Charlie is not a fan of spending time on his stomach. I think he has a hard time lifting up his heavy head and body! So he spends some of his time on the boppy so it's not such an unpleasant experience.
Tummy time often ends up like this - Charlie chewing on his hands or arms.
Charlie discovered his feet this week, and loves to grab his left foot when he's in the car seat or laying on his back.