"Trash, Mama"

Sam was eating lunch the other day after he had woken up from a nap.  I gave him chicken and made peas while he was working on the chicken.  When I offered him the peas (offer is what baby books tell you to do- instead of giving it to the child?), he shook his head and said, "no."  This is a new word for him and it is using it whenever he can.  So I put the peas aside and a few minutes later set the bowl of peas back down on his tray.  He looked a me like, "haven't we discussed this already?"
"No," he said a little more vehemently.  I retreated again with the peas (which he really does like).
When he finished his chicken I picked up the empty bowl and surreptitiously placed the peas back on his tray.  He looked at the bowl, picked it up and held it out to me, and told me, "trash."
He repeated it again, just in case I didn't hear him the first time.

He actually ate the peas in the end, despite his direction to throw them away.  I used to think he picked things up being around other people, but since I have been with him all summer, I am now wondering, where does he get it from?