Here's what you'll need:
#4 weight yarn in 2 colors
F/5 3.75mm hook
Stuffing or bell or crinkly plastic
Make 2 in Main Color
1. Ch2. 2sc in the 2nd chain from the hook. Ch1, turn. (2)
2. 2sc in each stitch across. Ch1, turn. (4)
3. 2sc in the first stitch, sc in each remaining stitch. Ch1, turn. (5)
4. - 10. Repeat row 2 until you have a total of 12 stitches on your last row.
Piece one: FO here.
Piece two: Do not FO.
Sandwith the two pieces together. Sc through both layers completely around to seam. Place (3sc) to make the corners. Stuff with whatever you want before completely closing. Finish crocheting together. Join with a slst to the beginning sc. Do not FO.
Chain ... a bunch... to make a string. I chained 140 but wished it longer but I am pretty tall, so maybe stand up and see where it falls? FO.
Loop the end around for a little handle for your finger and use the tail to sew it into place.
With a contrasting color, cut 10" fringe and tie them to each stitch on the edge opposite the 'string'. I secured with slip knots rather than as you usually add fringe because I figured this would stay on better.
Drag along the floor in front of your cat and see how impressed they are by your efforts.
Safety: This is a toy that I put away when I am not playing with the cat because I immediately saw the kitten spiral herself up in the string. Strings left for cats to play with unsupervised should never be more than about 10 inches long.