Beat the game.
Beat a level with "expert sneaking".
Found an Easter egg
Scored above 5,000 points.
Scored above 3,000 points.
Scored above 2,000 points.
Beat a level before the Bunnman arrives.
Escape from Ratman before he can toss you.
Meet the Bunnman.
Freedom to the cats!
Beat the tutorial.
Hidden Kitten! Played the bonus level hidden kitten.
Beat levels 1-16 in one playthrough.
Got all of the achievements for Cat Capacity.
Scootied through part 2 of the tutorial in 15 seconds or less.