Switchblade knives were popularly supposed to be capable of opening with enough thrust to inflect a serious stab wound.
Ridiculous on the face of it. First of all, switchblades opened the wrong way to provide ANY thrust at all, as they folded the sharp side inward, toward the clasp, and the point would not have been in position to provide any kind of penetration.
There was a variant, called a springblade, that rather than folding out, used a spring to thrust the point straight out of the clasp, making a straight-blade knife out of what had been a clasp, with the blade concealed within. This may or may not have had enough force to penetrate clothing or body tissue, but like blackjacks, brass knuckles, or slug shots, they are illegal almost everywhere, with severe penalties for even possession.
Apropos of nothing at all, there used to be an airline (once a railroad) called “Seaboard and Western”, or known as “SB & W”, which was translated as “Switchblade and Whiskey”.
A have my Great Grandad’s blackjack and brass knuckles for when he was a train conductor.