The reason why the butterfly knife was called the butterfly knife was because its body was very similar to a butterfly.
A butterfly had a body and two wings. When the wings were folded, it could wrap its body.
The butterfly knife was the same. The blade of the butterfly knife was the body of the butterfly.
If a normal knife was to be put in a sheath, the sheath of the butterfly knife was not a sheath. It had two sheaths, one on the left and the other on the right. When the two sheaths were folded, the blade of the butterfly knife could be installed.
The two scabbards were like the wings of a butterfly. They could be closed at will.
In other words, the difference between a normal knife and a butterfly knife was that the moment the butterfly knife was opened, the two scabbards could be combined to form a normal knife. It could also grab a scabbard and throw it out, to hold the other blade.
