I remember various USA states trying to ban the Buck folding hunters back in the 1970s.
I can remember that in one of their cases, I think it was in California, it was argued that they were switchblades because a police officer was able to hold one by the blade and open it by jerking it in the air.

The idea that you would be left holding the knife by the blade and threatening the other person with the handle seemed to be a consideration the officer missed.
(Notice my avoiding any pun on whether he got the point)