Motion sickness, also known as kinetosis, occurs when there is a disagreement between visual cues and vestibular cues. The brain becomes confused and causes nausea and vomiting. There are several theories that attempt to explain why motion sickness occurs, including that it is an evolutionary response to prevent the ingestion of toxins. In general, motion sickness can be reduced by keeping one's vision fixed on the external world to reduce conflicting signals to the brain.