Intro: K'nex Butterfly Knife/switchblade
I love flipping this thing around, it's addicting. XP
Anyway, pretty simple, may have even been done before.
Also, things that may be coming soon:
-K'nex pistol with ammo that goes in the handle
-K'nex Wrist knife (not very hidden though)
Step 1: Step 1
This is pretty much it...
Make two of those things in the picture,
these are the handles,
and add a gray connector to the black Y-clip.
then look at the title picture and you should be good from there.
If you do need more pictures, just tell me and I'll get one up for you. :)