The physical aspect of play is by far the most immediate aspect. When we play, be it a free-form of play or a more structured approach through games or sports, we use our body. Sometimes a lot, like when dancing, running, wrestling, or pretending to be dogs. Sometimes a little, like when playing chess or poker, where even the slightest movement of a facial muscle can be decoded into millions of meanings. The amount doesn't necessarily matter. Physicality is seen and interpreted by everyone, and is easy to relate to.