Hi Kiera,
What to do for signs like that varies with the concept but in
general you try to represent the concept visually in a way that
portrays the intended meaning. Often this is done by "role
playing" the animal, or using signs in creative ways.
For a cow "mooing" you could rear your head back and hold an "M"
near your mouth and then mouth a long "moo" as you change the
"M" into an "O" handshape and move the hand up and out into air.
For a bird clucking you would hold a "G" near your lips and then
mouth "cluck, cluck" while jutting your head up and forward like
a bird does. The letter G would start closed and then open with
each cluck.
Cordially,
Bill
(Dr. Vicars of
Lifeprint.com)