Sonic the Hedgehog is a 2D, side-scrolling platformer, whose gameplay centers around Sonic's ability to run at high speed through levels incorporating springs, slopes, high falls, and loop-the-loops. The levels contain hazards in the form of robots ("badniks" in the Western game manuals) in which Dr. Robotnik has trapped animals. Although destroying a robot frees the animal within, this is not required to complete the game. The player must avoid rows of sharp spikes, falling into bottomless pits, being crushed by moving walls or platforms, and drowning (which can be avoided by breathing air bubbles periodically released from vents). Sonic's main attack is his spin, where he curls into a ball and rotates rapidly (damaging enemies and some obstacles). This can be performed by jumping in the air or rolling on the ground.