common
Yes, "Karate" should be capitalized as it is a proper noun referring to the Japanese martial art.
In my experience, I found Tae Kwon Do to be a more advanced and proper martial art than Karate.
Clenching in surprise, usually with the anus
In normal situations karate is a noun and would be lower case. However, when coupled with a specific style it becomes a proper noun. I study karate. He has a black belt in karate. I study Shido Kan Karate. He has black belt in Shitokan Karate.
clenching fists
The word clenching means to tightly grip your hand or hands, to close or squeeze together or to clinch a bolt. Mostly it is referred to when using your hands.
Karate relates to science in the sense that with certain velocity's, speeds and time, the most deadliest of punches and kicks are created. It also deals with using proper mechanics such as using leverage, momentum, and distance.
No, you cannot put someone to sleep with a karate move. You can knock them out or render them unconscious with a blow, but they are not sleeping. It is too dangerous to attempt without proper supervision. Find a karate instructor who can teach you in a controlled and safe environment.
yes very big consinquence
if you are looking at this question, and it makes you wonder. Yes
Bruxism