My 2 week old chicks were doing it today when I put them out for a bit... They were all elbowing each other to get to the good spot and seemed to really really like it.. they made this little trilling noise and Im pretty sure their eyes were rolled back in their heads. They were cheesed when i scooped them up and put them back in the brooder box. First time I saw it though I thought they were having death throws or something, one in particular lays flat out and really gets into it... thought for sure she was spasing out.