Many scientists say there is evidence to support the idea that dogs do, in fact, experience dreams. Researchers using an electroencephalogram have tested canine brain wave activity during sleep. They've found that dogs are similar to humans when it comes to sleep patterns and brain wave activity. Like humans, dogs enter a deep sleep stage during which their breathing becomes more irregular and they have rapid eye movements (REM). It is during REM sleep that actual dreaming and, often, involuntary movements take place. Dogs may move their legs as if they are running, whine or whimper as if excited, and breathe rapidly or hold their breath for short periods.