313 cats were saved by this box-slinger on this day! :D
Visually, there's not much to look at. With an 8x8 tile restriction, it can be tough to fill the void, but something is better than nothing. In my submission, I used 2x4 pixel bricks of various shades of grey to break up the monotony of the background, and it goes a long way to adding depth.
For your sound design, you might consider randomizing the pitch of the audio clip by +/- 15% when a cat is collected, to add some variety to the otherwise repetitive meowing. To take it a step further, you could even randomize the clip entirely from an array of meowing clips.
Gameplay wise, simple and sweet. The yarnball is interesting because on one hand, I can nab a bunch of cats in one go, but on the other, I run a higher risk of dropping one. Played thrice to beat my score, so hats off to you there.
Good start, and good luck! :D