Play sessions took place in an indoor laboratory containinga cordoned-off play arena measuring 5.5 m × 3.5 m. This area included a door that opened into a small room in which the target dog was placed before the session began. Each session involved only the target dog and a single partner. On arrival, owners brought their dogs into the laboratory, placed them in the arena and remained with them until they had settled in. Once the dogs were relaxed,the owners left the laboratory and the target dog was released from the holding room. Two researchers remained to record the session and to manage the dogs. A pilot study indicated that dyads tha twere left alone in the arena tended to focus their attention on there searchers there searchers and so did not interact with each other. Accordingly,to overcome this, we spoke to the dogs or petted them until the yeither started playing or had ignored each other for 5 min. Datacollection took place between 6pm and 8pm, from June to August2011. We used a Samsung SD camcorder to document sessions and began filming once the dogs engaged with each other, either bycoming face-to-face and making prolonged eye contact or when one of the dogs sniffed the other. Filming was ceased if the dog shad not interacted with each other for more than five consecutive minutes.