Your stomach lining completely regenerates itself every 3 to 4 days.
If it didn't, the powerful hydrochloric acid your body uses to digest food would end up digesting your stomach instead.
Here is something most people don't know:
You have a "second brain" in your gut, and it actually produces more of your body's serotonin than your actual brain does.
It’s called the enteric nervous system (ENS). It's a vast network of about 100 million neurons—more than you have in your spinal cord—embedded in the walls of your digestive tract.
While your brain in your head uses serotonin to regulate mood, sleep, and happiness, about 90% of your body's total serotonin is actually manufactured and stored in your gut.
This is the biological reason behind phrases like "gut feeling," "butterflies in your stomach," or losing your appetite when you're anxious. Your gut and your brain are in constant, two-way communication (via the vagus nerve), meaning your stomach literally "feels" your emotions, and your microbiome can even influence your mood and decision-making.
So, when you make a tough choice based on a hunch, you're quite literally thinking with your stomach.
Sharks are older than trees.
The earliest evidence of shark scales dates back about 450 million years. Meanwhile, the earliest species that we would classify as a "tree" (like Archaeopteris) didn't evolve until about 350 million years ago.
This means sharks had a 100-million-year head start on trees, and they have survived four of the "Big Five" mass extinction events that wiped out almost everything else on Earth.