What you're not meant to do with the vaccination gun!
The blisters on my fingers made me change to operating the gun with my left hand, which was fine until a passing sheep (they were going through a conveyor machine - sooo much easier and faster than working in a yard race!) jerked its head up under my hand, causing me to run the needle across my right wrist. The faint parallel line on the left of the scrape is the vein that I narrowly missed. The visible damage wasn't all that bad, though not exactly comfortable, but I was a bit crook the next day when my blood pressure dropped as my body coped with the small amount of the vaccine that would have been on the needle. (It is not uncommon for sheep handlers to stab themselves - and occasionally other people - while vaccinating.)