The general version of the sign for cat starts with an "open F."
This handshape looks like a normal "F" except that the index finger
and thumb are separated by about an inch.
Place the "open F" handshape near the bottom of your nose and
move it out to the side while changing it to
a normal "F" handshape
The sign "cat" can be done using a "G" handshape that starts
near the bottom right of the nose and moves out to the right while changing from
a normal "G" handshape to a "closed G" handshape:
CAT ("G" version)
CAT ("8" version)
The sign for cat can even be done using an "8" handshape (instead of an "F"
or a "G.")
That version starts with an "open 8" and moves to the side and closes into a
normal 8 handshape.