Laughing in his sleep

I went into my son's room to wake him up this morning (its a call day for me, so I don't go into work until later in the day) and, right as I was getting ready to nudge him awake, he started laughing. Not an hysterical laugh like when I tickle him until he collapses; no, this was a good, round, hearty giggle-to-overt-laughter kind of thing. What a great moment. I've never seen anyone laughing in their sleep (and, of course, I think my son's got a particularly contageous one) and it startled me at first. When he stopped, I woke him and asked him what he was laughing at. He didn't remember, just "a funny dream, I guess." Praise the Lord for laughter--what other God would allow his people to laugh even while they sleep?