I saw a show on TV featuring ancient Chinese weapons, and one of the items they featured was a "Sleeve Arrow". It was a spring-powered arrow hidden in the sleeve of the wearer. A collectore supposedly had an authentic item, and he shot it at a dart board at a range of a few feet, and it barely penetrated the cardboard dart board. So how on earth can it be classified as a "deadly" weapon? Things to be considered are the level of technology at the time to produce a metal spring of enough power to drive a small arrow with enough velocity to kill, and can such a weapon be "cocked" by human force alone? Looks like somthing the Mythbusters should look into.

Setting aside any metallurgy considerations, anybody rich enough to afford one of these would probably be able to afford someone to cock it for him.

I saw the same thing.
I liked the Flying Guillotine.

How is it deadly?
Hitting certain area's , eye , carotid artery , really anything that pumps excessive amounts of blood. Axillary artery etc..
Any place soft that the arrow moving so slow could pierce so easily. Jugular! ... maybe it's not as easily to sever a head as many people think, so the dart may just cause extreme annoyance