Burrs are traps in Skyward Sword.
Burrs are usually found attached to ropes, but can also be found on the ground hidden among grass. If they come in contact with Link, they will attach to him, flashing red with an increasing frequency before finally exploding. Though their explosions deal little damage, if Link is on a rope he can be knocked off. Burrs stuck to Link can shaken off, for example by swinging his sword. Burrs can be detached from ropes by shaking the Wii Remote to make Link jostle.
Burrs on a rope and among grass in Faron Woods