Officials and specialists are still puzzling over how a Siberian tiger managed to escape from its enclosure in the San Francisco Zoo, killing a visitor on Christams Day. A story in the Boston Globe reveals that the vertical wall of the enclosure was only 3.8 meters high, while one expert states that a full-grown tiger can reach that height with its front paws simply by standing on its back feet. The guideline wall height recommended by the Association of Zoos & Aquariums is apparently 4.8 metres.

The San Francisco Chronicle is collecting reader comments on this tragedy.

This is by no means the first time that big cats have escaped by leaping their enclosure walls. In November we reported how cheetahs at the St Louis Zoo in Missouri had managed to scale a 3-metre wall three times in the same exhibit since 2000.

CNN has a somewhat grisly list of further zoo escapes and accidents.