I have always heard when they are staring into space laughing, that they are watching the Angels dancing.

They can see stuff we don't. My DS will sometimes laugh at nothing, but it really seems to me like he "sees" something. My husband got freaked out one night because he looked up at the ceiling laughed and waved. LOL.....I told my husband the "wave" was involunitary.

I also heard when they smile in their sleep, the Angels are wispering to them.