The brown stuff is called plaque. This forms on your teeth when you eat and its something you can't get rid of. There is tooth paste that can help maintain it.
When stimulated, the brain stem's sneeze center orders muscle contractions from esophagus to sphincter. That includes the muscles controlling the eyelids. Some sneezers even shed a few tears. Perhaps people close their eyes while sneezing to prevent the expelled particles from entering their eyes,
Ask google, it’ll tell you
Answer: The automatic response to tensing your muscles after you hear the sound of the clanking the rollercoaster makes is an example of the phrase pavlov's dogs, which can refer to classical conditioning because it refers to the habit of automatic response to a stimulus.
A set considered the amount of repetitions that were completed in one exercise. A repetition is the each individual time that the person doing that exercise.
Example: I do a set of 4 bicep curls. Each set will be 10 repetitions. That means I will do 10 bicep curls, 4 different times to total 40 bicep curls.
