Things I've learned from leather working
Water based dye doesn't mean it cleans up really well with water
When pounding on a hide, make sure objects on the top shelf of the workbench are secure, or at least not heavy!
An uncovered pricking iron will usually find a fingertip when reaching for another tool in the rack.
Any spill of coffee, soda, or water will always find the piece you're working on.
Cats can make a HUGE mess on the bench if you come into the room and scare them.
The needl
Probably shouldn't admit this for two reasons: there has already been enough blood and this lesson learned is far too serious, but here it is anyway.
Never put a knife down on the bench without it's sheath and a corollary (that's something that follows logically from the first part), never cut leather in front of a customer!
I was trying to be a nice guy, the customer was a pain. He wanted his holster his way, i.e. his pattern. And he wanted me to do the initial cutting where he could see it