I saw several big tough Marine Recruits faint at the sight of a hypodermic.  Some of the biggest baddest muthas in the platoon could not stand to get their shots. 

I still carry scars on my forearms from where I flinched when the trigger on the pneumatic inoculation gun was pulled.  That's probably the only time some of those Corpsmen ever pulled a trigger.

Click on these photos and see what I mean.