I used 3 colours of worsted weight yarn and a size E (3.5mm) hook for my pattern. You could use as many or as few colors as you like! If you use a slightly larger or smaller hook, the size of the spaces between your stitches (and the size of your overall mouse) would either increase or decrease proportionately. You may wish to altogether avoid weaving in your ends for this pattern, as it gets harder to do as you close off the body, and they will be hidden on the inside anyways!

I hope your cat enjoys his or her new toy!! =^_^=