It can be disconcerting to new dog owners when they discover their pooches whimpering, shaking or seemingly crying in their sleep. Although there may be some rare instances when this behavior is linked to pain and distress, by and large it is a natural response in many animals when they doze off. Although there is no exact way to measure what is going on in the pup’s mind, experts like Dr. Bonnie V.G. Beaver, DVM, author of Canine Behavior Insights, says the main reason that dogs produce noises in their sleep is that they are probably dreaming during the REM phases in their sleep cycles. Dogs, just like humans, have the potential for vivid dreams while sleeping, as evidenced by looking at dogs’ brain waves during REM sleep. During these phases, dogs may show movement like wagging their tails, twitching their paws, fluttering their jowels, or making noises like whimpers. In some cases, dogs also may bark while sleeping, says PetMD. Pet owners should rest assured that very likely these vocalizations and movements are completely normal. However, if they are new behaviors, it could be worth a discussion with a veterinarian. Also, new pet owners should know that a dog who makes noise while napping, may also do so during the night, and should not be overly concerned if they are woken from bed by pet noises. The general consensus is to simply let the pooch be as he or she works through those REM stages.