This photograph shows a giraffe with an impala skull in its mouth. From the photo alone the motivation is unclear, but there are extensive records of giraffes engaging in osteophagia, or bone eating.

When you're that tall a little extra calcium comes in particularly handy, but lots of other animals engage in osteophagia on occasion. Bones are a rich source of phosphorus as well as calcium, and animals don't always fit into the neat carnivore, herbivore, omnivore categories we learn at school.

Despite the name, osteophags seldom eat the whole bone – particularly when they come from animals of similar size. However, by gnawing on bones, antlers or even ivory they can get the nutrients they need.

Reports of large ungulates gnawing bone have been summarized in the Journal of Archaeological Science . Nevertheless, the process remains somewhat mysterious, with one study finding that the fluids within ruminants' stomachs would not be able to draw out significant amounts of minerals . Giraffes do seem to do it more than other ruminants, however.

Some giraffes are more prone to exotic eating than others. Tony, a pure Rothschild's giraffe at Werribee Open Plains Zoo in Australia was notorious for eating dead rabbits in front of visitors. “It just ruined your talk,” says Goldie Pergl, former visitor experience officer at Werribee. “You'd explain how giraffes were herbivores and he would do that. Then he'd come up and start eating the rubber off the windscreen wipers, which puzzled us even more.” Other giraffes at the same zoo were far more likely to stick to the script.

The photo is one of many superb images by Rene van der Schyff of African wildlife near her home. Facebook

However, if you'd prefer some live action see below.