A, You Can't Tell People What to Dream About

There's research which you can influence what people are dreaming to some extent. And as you mention, this can't exactly be tested in a laboratory setting. Just like with dreams, you can't force some one to have a dream and then study it. If you play soft music, particular music, it could be that the person reports a dream which somehow contained that music. It does happen at somee. A, not always its is dependable, but it does.