system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do sharks sense/smell blood in the water so quickly and efficiently?
gpt
Smelling is a shark's primary sense. Their nostrils are on the outside of their body, and they only use them for smelling not breathing. Water continuously flows through a sharks nostrils interacting with highly sensitive membranes that feed information to the shark's brain. This information allows a shark to pinpoint the source of blood.