K, good guesses by everyone. Unfortunately you were all MILES away. I thought it was obvious.
It's one of the top flaps from a box of mac & cheese that Max got ahold of. I don't know how long he had it in his mouth, but when I went to change his diaper and layed him on the changing table I could see some big hunk of something stuck to the roof of his mouth. It was pretty sick.
And the green thing is a pea that I gave him about an hour before.
What a guy.