Stella can really sleep hard sometimes... and sometimes she twitches, sometimes she makes little chirpy noises, sometimes we get both and then of course, sometimes nothing... Last night, when I heard a couple deep heavy sighs from her while napping... I brought the video out... it was a twitchy nap! It's normal for dogs to do this and it looks like REM sleep to me with the eye movement. It didn't last long and then she was off to stillness dreamland..
Website about movement and noises in sleeping dogs - movements-and-noises-in-sleeping-dogs-8907