How can you possibly rely on your visual sense to point a needle at something which you can not see? Welcome to the wonderful world of arterial line placement where tactile aiming is king. Extend the wrist, feel that pulse, and stab in the dark. A bright flash is all you need to know you hit the bullseye. Be careful and holster those two digits of yours, you're a sharpshooter now.
Inspired by "1000 Awesome Things".
(Image from Gare and Kitty via Flickr)