The sign for "sit" uses a single motion. This is part of a noun/verb pair. If you use a double
motion it means "chair."
Think of the right hand as representing the legs of a person. If you
were to show that person shifting uneasily from side to side in a "chair" it
would mean "anxious." You can sign ANXIOUS by holding your hands like
you do for the sign "SIT," then twist your dominant hand to the right and
then to the left so that your index and middle finger alternate being lifted off
of the left "H" (palm down) hand a couple of times.
Click here for an example: YOU FEEL ANXIOUS, WHEN? (When do you feel anxious?)
Note: A "small animal sitting" would not use the traditional "SIT" sign. Instead
you would use a "bent-V" hand.