Zoos will put things in ice for the bears to use their predominate hunting skills and allow them something to play with. Believe it or not they love LOVE ice and they really enjoy getting food items in the ice. I guess maybe they are used to it or something of that nature. I worked at a zoo in San Diego part time and it was interesting talking to the people working with polar bears in a hot climate they kept it cool and stuff but they had to be inventive.