Maracas have a handle you hold and a bulb at the end that is full of seeds or something else small and hard. When you shake them, the seeds hit the side of the bulb and it makes a distinctive noise. Maracas can be made of wood, leather, metal or plastic. They sound different depending on what they are made out of. Maracas that are made especially for a baby, usually out of plastic, tend to be called a rattle.