You will need:
A piece of cardboard
Sorry I could not put everything in the picture.
Step 1: The ears
Fold in-half a piece of black fabric (WARNING: make sure you fold it so the ugly side is facing out. Fold it pretty side to pretty side!) and then sew the long side down (WARNING: Make sure the fabric is the right size for your ear's). Now turn the ear inside out. Once you have 2 like this stuff them with your stuffing, stuff them very full so that they stick up when you sew them onto the hood of your sweater.
I didn't have a sweater I am just using a green shirt so I don't have a hood to sew them onto, sorry. The last step explains.