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Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
The shortest mature adult human of whom there is independent evidence was Gul Mohammed in India. In 1990, he was measured in New Delhi and stood 22.5 inches tall.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
For about 100 years, scientists thought that peptic ulcers were caused by stress, spicy food, and alcohol. Later, researchers added stomach acid to the list of causes and began treating ulcers with antacids. Now it is known that peptic ulcers are predominantly caused by Helicobacter pylori, a spiral-shaped bacterium that normally exist in the stomach.
Bacteria have been found alive in a lake buried one half mile under ice in Antarctica.