Answer: Adrenal gland
Explanation: It is an automatic response known as the 'Fight or Flight response, that is stimulated by our adrenal gland that is in our endocrine system produces adrealine.
These glands are located above the kidneys, and they secrete adrelaine when a person is angry or afraid. As in this situation, you see that the person is most likely to be afraid.
Adrelaine causes increase in heartbeat and blood pressure, and produces other substances for instant energy. This is when the situation, as mentioned before, 'Flight or fight situation' comes in hand, which is, it prepares the person to run away, or to fight from a dangerous situation.
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