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