knife

KNIFE:

This sign looks a lot like the sign for "CAN'T" but there are some differences.
In the sign for "can't" the right hand starts palm down, moves downward and whacks the third knuckle or tip of the left index finger very quickly.  The left index finger bends to let the right index finger past in its downward movement.

In the sign for "KNIFE" the right index finger starts with the palm facing backward and moves down and contacts the second knuckle of the left index finger then makes a small backward slicing movement as it continues its downward path.

Animation: KNIFE (version 1)

In this version, the knfe moves down, contacts the "carrot" and the slices forward along and off of the carrot. As if peeling a carrot.

Animation: "KNIFE"

"Cut with a knife"
This sign looks like you are using your right index finger to saw  your left index finger off.

Animation:  "Cut with a knife"

Here is a version of knife that uses an "H" handshape on the dominant hand instead of just an index finger.  This sign means "KNIFE" just the same as the other version, but I reckon if you were talking about different types of knives, you could use the "H" handshape to show a knife that is larger than a knife done with just the index finger.