Gorillas play "tag" in a similar way to humans, scientists have discovered.
By studying footage recorded in zoos, the team found that the great apes would hit a playmate and then run away, chased by the gorilla they had struck.
Occasionally, the roles would then reverse, with the chaser hitting back, and then getting chased.
The research, published in the journal Biology Letters, suggests the primates are testing the limits of acceptable behaviour within their social group.
Marina Davila Ross from University of Portsmouth said: "This shows a strong similarity to the game of tag in children.
"We cannot say it is exactly the same as the game of tag, because games involve rules and the individuals need to be aware of these rules, but the behaviour does looks similar."
Hit and run
The researchers looked at footage of playing gorillas taken from five zoos, which had been recorded over a period of three years.
Dr Davila Ross, who carried out the research with scientists from the Free University of Amsterdam, The Netherlands, and the University of Veterinary Medicine Hanover, Germany, said the team found examples of this behaviour on 86 occasions.
She told BBC News that the films had enabled the researchers to study how the apes would respond to an advantageous or disadvantageous scenario.
She said: "That was really interesting - hitting represents an inequity.
"When you hit someone that represents an unfair situation. Because of this, it allowed us to assess for the first time how animals respond to an inequity in their natural social setting."
She added: "We found the hitters moved first and ran away - it was a hit and run behaviour. And this indicated that the hitters created for themselves an advantage and they tried to keep this advantage."
She said that this implied that the gorillas were capable of changing their behaviour in unfair situations.
The researchers also found three occasions where the gorillas did not run if they had hit another ape very gently, suggesting that they could judge how roughly they were playing, and alter what they do next accordingly.
Dr Davila Ross said the hit and run games could help the animals to learn how to better judge social situations.
She said: "It seems to me that they can learn through this kind of behaviour about limits and how far they can go in a social setting, and also about their specific group members and how far you can go with them."