The actress spends a lot of time in the water, surfing and protesting the killing of dolphins and whales - and she reveals she often finds herself swimming with sharks.
She says, "I tend to attract them everywhere I go... I'd really rather not see a shark while I'm paddling on a board... but, if you want to see a shark, put me in the water."
And there's one encounter she'd like to forget - she attracted one shark by peeing in the ocean off Hawaii.
Panettiere was diving with her mother and brother when was caught short and decided to relieve herself while treading water - but the relief was replaced by terror.
Appearing on late-night U.S. TV chat show Jimmy Kimmel Live!, the actress recalls, "This safety diver got in to take pictures of my brother and my mum and they had their fins on and when the shark comes too close, you put your fins in their face, and I didn't have my fins on and all of a sudden... they start going, 'Shark, right behind you!'
"I was going, 'What could it be? Tiger shark, Mako, bull, Great White...' I swam for my life... They were yelling at us because it's the worst thing to do is to swim away from the shark and make all the splashing. I was like, 'Guys, you yelled shark... How else do people react? I practically walked on water back to the boat.'"