I had to fight pretty hard for this cel on eBay.  
It's from Red Eyes (ep. 6 of the OVA), after 
Priss has been stabbed and had one of her railgun 
needles shot back through her shoulder, but 
before she REALLY gets the crap beaten out of her 
(luckily, she pays Largo back in spades).  
Definitely one of my favorite cels ^_^