Do aliens use knives?

The shape of a knife is determined by it's tasks and the environments in which it's used.

For example, the cutting edge is made of durable alloys of iron and is best suited for work on macroscopic objects in temperatures starting with 0C, and the shape of the handle is well suited for a block-traction muscle manipulator, which is our hand.

If the hand was ten times bigger - the taks and the shape of the knife would change. It would be shorter and wider, and would be able to cut trees in one swipe.
If the temperature was much lower, the knife would probably resemble a saw.
Or if it was much higher than the usual for our planet, knifes would probably be made of stone or high-melting metals. Tho who (and what) would need to cut anything in a temperature of -20C, or +500C?

I want to say that there are always the limits established by the fundamental laws of physics and chemistry in which we, as a class of matter, are able to exist. Those boundaries, it seems, are not that wide. And those limits, at the end of the day, establish the optimal shape and form of all objects and creatures. 

And I believe the that the span of said boundaries is not much wider than the span of our imagination.