Lexi and Betty are best friends. The two of them can play the whole day through - and they have!
Here is Lexi in the "Let's Play" position. Anyone with a dog will recognize this pose. Not everyone understands what constitutes "playing" for dogs, however, and with good reason. Playing, for a dog, is a bit like practicing their life skills. Different breeds have been bred to have specific skills; retrievers are bred to retrieve things, pointers point at things, herding dogs herd things, etc. These same behaviors are used when they are interacting with other dogs for the sheer fun of it, which is as good a way as any to define "play".
Not all breeds enjoy doing the same things. My two terriers are completely uninterested in retrieving balls, for instance. Terriers were bred to chase down and kill vermin, so Socrates and Lexi enjoy chasing and fighting. To complicate things even further, dogs like Socrates and Lexi are mixed breeds, and each has an unknown genetic heritage. What this means is that they have an unknown mix of skills. Betty is also of unknown origin, but Betty and Lexi also like to chase and wrestle. When they play it often looks a lot like they are fighting to the death!
They are actually having a great time "pretending" to kill one another. What is interesting is that Betty and Socrates don't play this way; Betty will roll over immediately if he ever tries to play. There are only a few dogs Betty will play with.
With Lexi, though, Betty gives as well as she gets! That's one scary face on her, isn't it?
When things get too rough, Betty has a unique method of calling a time-out. First she digs a hole in the dirt . . .
Then she lies in the whole and refuses to interact with Lexi or with anyone.
Betty stays in her little "den," until she is composed and ready to return to society. It is really a sophisticated and complex group of behaviors that allow her to call a halt to unacceptable interactions while allowing her to calm herself. As far as I know, it is behavior unique to Betty.
I may be wrong about that, though, because I don't know what breeds make up her heritage. She looks a bit like a Carolina Dog, a bit like a black cur, or maybe a red cattle dog. She has some herding dog ancestry, for sure. She will often do the "Crouch/Stalk/Stare" like a Shetland Sheepdogs when she is playing, which is another example of playing as practice for real life. Of course, isn't that true for all animals - including humans? I think so, but I'm no expert. I just enjoy watching dogs interact. To me it's intensely amusing and endlessly fascinating.