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An adorable video has emerged of a sleepy dog wagging its tail in her dreams. It must be a great dream because it is definitely making Ruby very happy. Watch as this happy dog wags her tail in her sleep. She is probably having a lot of fun in her dream! Cuteness overload! Tail wagging means a lot more to a dog than ‘I’m pleased to see you’. A wag to the right signifies happiness, and a wag to the left fear. This dog behaviour reflects what is happening in their brain. Scientists have also discovered that dogs signal to other dogs via their tails in ways hidden from humans. A secret dog language, incredible, right? Dogs are such wonderful, friendly, generous and lovable creatures who look even more adorable when they are sleeping, and this video is the perfect proof of that. Watch as this sleeping beauty travels to dreamland on a fast train, causing her to spin the tail like a windmill! Watch closely as this happy dog constantly wags her tail in her sleep! Lovely! The most common misinterpretation of dogs is the myth that a dog wagging its tail is happy and friendly. While some wags are indeed associated with happiness, others can mean fear, insecurity, a social challenge or even a warning that if you approach, you are apt to be bitten. Sometimes tail wagging serves the same communication functions as a human smile, a polite greeting or a nod of recognition. Smiles are social signals that humans use in situations where somebody is around to see them. For dogs, the wag seems to serve the same purpose! In addition, dogs' eyes are much more sensitive to movement than they are to details or colors, so a moving tail is very visible to other dogs. So, the next time your dog wags its tail don’t forget to pay closer attention to the encrypted message!