I don't think this is true. I believe there have been studies done that say that many mammals have the ability to laugh and do so often.

It seems at this time there was quite a bit of differentiation between "boys' games" and "girls' games." It feels contradictory that on the top of this page he used the example of "a little girl playing ball." Wouldn't spoil-sports be present in girls' ball games?

What does magic circle refer to? Why is it included in this list when all the others are real, physical places?

Could gambling addictions be considered an inability to suspend play?

Aside from being used in daily life, these topics are also very prevalent in modern games.

With today's scientific knowledge, I would equate this to the release of dopamine and other neurotransmitters in our brains during play. It is part of the reason we “enjoy” play and also incentivizes the next instance of play.

This theory was really interesting to me because it could have very different meanings for humans and other animals. For animals, roughhousing as a youth could prepare them and help build experience for fights over resources as an adult. For humans, our early childhood toys consist of things like matching shapes, completing simple puzzles, music makers, etc. This seems more suited to learning logic and fine motor skills--important skills for human adults.

If we can assume by the sign-off that he began his book in 1938, and then published in 1944, that would place us in Switzerland during Nazi Germany and the beginning of WWII. I wonder if any of his writings in this book were influenced by current events and if he considered war strategy as a form of play. It is easy for us to think of war as play, but for those who lived through it, it may have seemed like an outrageous statement.