People are prone to anthropomorphise (fabulous word!) animal behaviour, which is why they like to think that some animals kill for 'fun'.
I doubt that any animal understands the concept of 'killing for fun' - they kill because it is in their survival instinct to do so.
The most popular misconceptions is that foxes run riot in hen houses for 'fun', but as Sir DA advises, an fox undisturbed will take away all the kills and bury them for future consumption.
Cats 'toy' with prey to hone their hunting skills, not for the sadistic pleasure of torturing another animal.
People need to remember that animals are not like us in many ways, at all, even though we would like to pretend that they are.