Do Koreans really say things like this?

This is the beginning of a list of expressions I come across that seem a little strange to me and that I am a little suspicious of. As I get answers, I will write "Solved" and what I have learned under each expression. Please feel free to comment.

• 발에 땀이 나도록 뛰다 -- Run until your feet sweat.
  .
  SOLVED: I thought this expression was strange because we do not have to run very far for our feet to start sweating. I have learned that this expression probably came from 개발에 땀나다, which means "sweat on a dog's foot." Dogs do not really sweat except for places like around their ears and on the pads of their paws, but a dog would have to run pretty hard before one would notice the pads of its paws sweating, so Koreans use 개발에 땀나다 to emphasize that someone is doing something, such as working or running, especially hard. The following is an example of how it can be used:
  
  * 개발에 땀나겠다. 좀 쉬어가면서 해라.
  A dog's paw would sweat. Do it while taking some breaks.
  ..
• 머리에 쥐가 나도록 뛰다 -- Run until your head cramps.
  
  SOLVED: 쥐 means "cramp" or "charley horse," so the above expression seemed strange since I had never heard of someone getting a cramp in their head. However, I have been told, and one of our commenters has confirmed, that 머리에 쥐가 나다 does not refer to a physcial cramp, but to a mental cramp. In other words, it is used when someone has a perplexing problem weighing on his or her mind. Therefore, I think 머리에 쥐가 나다 could be translated as, "I have a problem that is bothering me," which suggests that it was used inappropriately in the above sentence.
  
  Apparently, even some Koreans are confused by the expression, judging from comments HERE, HERE, and HERE.