Talking in his sleep

Emmett occasionally yells in his sleep. Sometimes he's waking up, and sometimes he's not. He's always quite agitated. Here are two recent examples:

I don't want you to put it away!!! I don't want you to put it away!!! ...

Where is the last cookie??? Where is the last cookie??? ...

In a soothing voice, I tell him what he wants to hear (we'll find the cookie, honey, and if we don't we'll make some more), and he usually goes right back to sleep.