Tricky plurals
Why is the word "pants" plural?  Some people say it's because pants contain two pant legs, hence a "pair of pants."  But my shirt contains two arms; does that make it a pair of shirts?  No. 

This is an example of a tricky plural.  Other examples include a pair of scissors, a set of eyeglasses, and underwear. 

Also related:  A "TV set" is so called because apparently the components used to come in a set, and the user had to put everything together. #language

Blood-injury phobia
Something like 15% of humans experience blood-injury phobia, a.k.a. passing out at the sight of blood.  I'm tempted to think of these people as weak or "maladjusted", but in reality they have a psychological condition that's as much their fault as something like cancer or depression.  The interesting thing is that this phobia can be coached out of a person through something called applied tension, which consists of clenching your muscles whenever you're about to faint, which raises your blood pressure. #health