Emotion, in everyday speech, is any relatively brief conscious experience characterized by intense mental activity and a high degree of pleasure or displeasure. Scientific discourse has drifted to other meanings and there is no consensus on a definition. Emotion is often intertwined with mood, temperament, personality, disposition, and motivation. In some theories, cognition is an important aspect of emotion. Those acting primarily on emotion may seem as if they are not thinking, but mental processes are still essential, particularly in the interpretation of events. For example, the realization of danger and subsequent arousal of the nervous system (e.g. rapid heartbeat and breathing, sweating, muscle tension) is integral to the experience of fear. Other theories, however, claim that emotion is separate from and can precede cognition.