Penny Palfrey saw groups of hammerhead sharks during the last part of her 41-hour Cuba-to-Florida attempt over the weekend.

A large intimidating creature with a distinctively shaped head, how dangerous is the hammerhead to humans?

According to the authoritative International Shark Attack File that tracks shark attacks since 1500, there have been 21 unprovoked attacks of hammerheads on humans that have resulted in 2 deaths.

While the number is considerably lower than the attacks and fatalities caused by the Great White Shark, bull shark or tiger shark, hammerheads are still considered potentially dangerous.

Hammerheads often live close to shore swimming along the surface with their fins exposed over continental shelves and in inshore waters including bays and estuaries.

In some parts of the world (Yonaguni Island), they form large groups, but adults generally swim singly or in small groups unless they gather together in schools during migrations as seen by Steven Munatones during his circumnavigation swim around Yonaguni Island.

Singly, in small groups or massive pods, swimming over or near a hammerhead is an unforgettable experience.

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