Froak is an enemy that appears in Skyward Sword. Froaks damage Link on contact using the spikes that cover their bodies. Froaks resemble a puffer fish, albeit puffer fish which can float. Link needs to use the Gust Bellows in order to blow Froaks into walls, which makes them explode. Another effective strategy is to fly the Beetle directly into them.
The Sand Froak will float around aimlessly with a smooth body, but when you draw near it will shoot out the spikes surrounding its body. It will continue to float, but this time towards you, and will damage him if it makes contact. Froak will explode when attacked or killed, so the sword is not the best way to deal with them. It is better to either use a long range attack such as the Slingshot or Bow, or to use the Gust Bellows to blow them into a wall.
These water-based blowfish enemies can be found in Lake Floria. They are like their sand brethren, floating around almost aimlessly until you draw near. Link can kill these enemies by using a spin to hit them into a wall, causing them to explode.