A Sumatran Tiger tears apart a wrapped Christmas present at Taronga Zoo on December 21, 2011 in Sydney, Australia. Animals received Christmas themed enrichment foods as part of the Zoo's regular program to encourage the animals to forage for food and help improve hunting abilities. (Photo by Brendon Thorne/Getty Images)

Seals eat Christmas treats at Taronga Zoo on December 21, 2011 in Sydney, Australia. (Photo by Brendon Thorne/Getty Images)

A Sumatran Tiger cub investigates a wrapped Christmas present at Taronga Zoo on December 21, 2011 in Sydney, Australia. (Photo by Brendon Thorne/Getty Images)

A Western lowland Gorilla eats popcorn from a bucket at Taronga Zoo on December 21, 2011 in Sydney, Australia. (Photo by Brendon Thorne/Getty Images)