Cogs are collectible items in the second game. There are totally four cogs that can be found and they are connected to primary events, making it obligatorily to find them in order to progress in the story. Every cog is used at least twice in the game, forcing the player to backtrack to get back every cog for the Tiny Tomba/Mini Tomba event.
List of cogs
Found in the Circus Village and obtained after the Use the Seesaw! event. It used in order to extend the bridge in the town. Fetch the circus ball, lead it to the seesaw and smash it with the hammer to make it fly up to the second floor. Repeat this on the seesaw there to knock down the bird holding the cog in order to obtain the it.