I'm not saying my gameface is pretty, but these pictures of people playing video games are hilarious. From now on I'll be gaming all alone, far from a camera. Photographer Phillip Toledano took these way back in 2002 in an effort to capture "[c]haracteristics that are usually secreted from the world." I'm going to say he pulled an epic pwn, at least in this round. You can check out the rest on Flavorpill. Link
Image: Phillip Toledano
Human emotions are expressed pretty much by every single part of our body. There is a good amount of stress involved while playing.
http://www.youtube.com/watch?v=PYQhvW-tjNM
I would suspect that as well. It is interesting to note that the vast majority of video games are simulations of war, killing, hate, anger, violence, etc...
Some of the reactions, those of elation, may be of people playing Mario Bros or something, but keep in mind that even Mario Bros is essentially a violent game wrapped in rounded character models with simple shapes and colors. This gives the appearance of something else, but the dynamic is still Good vs Bad in a bloody battle. Even if it only dimly appeals to humanities desire to kill, it is still the main force of the game-play.