Biology
How does your stomach avoid digesting itself?
Quick fact
Stomach acid (hydrochloric acid) has a pH as low as 1.5, but the stomach lining secretes a thick bicarbonate-rich mucus that protects the tissue from digestion.
Why this is interesting
Your stomach produces acid powerful enough to eat through steel, yet it doesn't consume itself—thanks to a microscopic layer of mucus that's constantly being rebuilt.