Friendly & not so friendly: Once two have finished smelling each other you will be able to notice if they approve of each other or not. If one of the has, it will be evident he wants to play, if the other didn't he will stand rigid and tense. When this happens the "playful" one will usually try to incite the "rigid" one by placing his front elbows on the ground while keeping his behind upwards. This is a classic sign of wanting to play.
Dog playtime: When a dog places his front elbows on the ground while at the same time keeping his bottom upwards, it is a clear sign and invitation to play. Dogs show this signal to otheras well to humans. The dog will usually maintain in this same position for a few seconds, while at the same timewagging his tail furiously, before he starts jumping forward and starts running, looking over his shoulder to see if his invitation to play has had any positive and successful results.
Dog chat: In comparison to human beings,posses a limited capacity to communicate by using sound and they tend to trust in their body language more to get their message across to a chosen place. The different types of sounds they make are used to help back up their body language more then when they are alone. Howling and growling are the least communicative sounds, however, barking is a tool they frequently use which are emitted in many different ways and which are used to transmit different meanings. These barking noises vary depending on if it is a guard dog that is trying to get attention, or if the dog is just trying to let off some energy or frustration.