Today, I made a Lego butter fly knife:
I will show pictures if you want to make it.
It takes 8 parts and 10 optional parts:
If you are going to make, this the two beige connectors are important to use because they are free-swivel parts so the blade can move freely. The other connector should be blue or black so the top blade stays in place. First, take the 3×1 beam and connect the three connecters like this: 
Then attach the two 15×1 parts on the two free swivel connecters:
When Attaching the 9×1, make sure there is one remaining slot on it: 
Then connect the second 3×1 on top of the connecters, which will finish it:
You can also now add the optional parts, which will make it solid. You can choose any color you want. You’ll need four 6x1s, four 8x1s, and two more 6x1s and put them on like this:
The Costume Kid 