What do these piranha fish have in common with an underwater elephant? Answer below
Both the African elephant and the Brazilian piranhas are unpaid extras in the BBC's latest blockbuster Planet Earth, which starts this month.
This series from the Natural History Unit, which took four years to make, promises to follow the mighty Blue Planet as
a must-see for anyone who appreciates the natural wonders of the world and great camerawork.
There should be plenty for divers to enjoy in the first part of the series - though the second part, which starts in autumn, promises to be the richest in underwater footage.
Firsts for the film-makers include packs of more than 100 sailfish hunting in the open ocean; a new species of blind cave angelfish in Thailand; pink river dolphins herding fish in the Amazon and presenting stones as "gifts" during courtship - the only known use of tools by wild dolphins; crab-eating long-tailed macaques deep-diving; and swimming hippos.
Producer Mark Brownlow and cameraman Peter Scoones were assigned to diving with wild red-bellied piranhas in Brazil's Pantanal, the world's largest wetland.
Filming these fish in the wild had never been done before, and was reckoned to be the greatest challenge of the series.
They look mild enough in the picture, but piranha are considered the most dangerous freshwater fish, and their wetland habitat is constantly shifting between being flooded and dried-out, which left only a narrow band of time in which the water would be clear enough for filming. Scoones was warned by the local guide not to venture too far into the gloom beneath the dense mats of aquatic vegetation - and not to stay still for long!
After three weeks of frustrated searching, Scoones finally found himself immersed in piranha frenzy as a school locked onto an injured fish, and stripped it to the bone in less than a minute. Relaxed enough to use ungloved hands to work the camera, he came back with some stunning footage.
The conclusion was that piranhas, like other "man-eaters", are dangerous to humans only in exceptional circumstances.
Peter Scoones was also responsible for filming the diving elephant shown above, in Okavango, Botswana.
As flood waters arrive in Angola, herds of buffalo and elephants trek along ancient dusty routes to reach the flood. When they are joyously reunited with water, they really get into it!
Planet Earth is the first natural history series to be filmed entirely in high definition, to provide "an unparalleled view of awe-inspiring landscapes from all across the globe and incredible footage of the rarely spotted, almost mythical creatures that live in these habitats". The series is produced, like The Blue Planet, by Alastair Fothergill and narrated by - who else? - David Attenborough.
Keep your trunk above water! An African elephant enjoys a swim