How does a shark find its dinner in a huge dark ocean?
Its nose is extremely sensitive to smells carried through the water — it can pick up the faintest trace of blood from a long way off, then follow the scent to its source. Up close, it even feels the faint electric crackle of a hidden animal's muscles.
From But WHY?! (p.79) — one of 162 illustrated answers for curious kids aged 7–12.