There is a common rumour that keeping a light switched on is more efficient than turning it off and on to save energy, claiming having it heat up again takes ages. Keeping a light on will only be more efficient if you only plan on keeping the light off for 5 seconds or less.
Gum does not take 12 years to digest. The reason the gum keeps hard in your mouth is because you keep chewing it, making it form new bonds again and again. If you stop chewing gum (I have fell asleep with it in my mouth) it dissolves to smaller pieces and eventually totally dissolves. I have often woken up with a minty gooey mouth with tiny white bits everywhere!
Your face will never stick to one expression, I dont know the true origin of it, but you may want to look up tetanus. The infection itself could cause spasms causing peoples faces to contract into grotesque expressions. Perhaps, in the days when people did not understand the cause, they blamed pulling faces on the infection itself.