Animals.
According to some Hollywood urban rumor, a great actor said: "Never work with children or animals. They will always upstage you".
And I believe, we can agree to that,because whenever an animal is in a scene, we tend to notice the animal more than the actor/actress that may be playing.
In my personal opinion, that was the reason that the first successful animation known to us that become a huge success was in fact a mouse that behaves and lives like a human.
A film with animals usually is a a box-office to be, a certain hit. If it is especially about the relationship, the bond between humans and animals it is even more touching and gets more attention form audience.
For example, who doesn't remember Lassie? The famous Rough Collie dog, faithful and intelligent lived together with her humans and animals companions and saved them when the occassion arised. If my memory serves me, the first film of Lassie was "Lassie come home" in which the Collie dog was sold to a rich Duke and wanted to return to his real "owner"*, the little boy of the family that had Lassie as a pet in its house.
Lassie has to travel a long way from Scotland to get to England, met a lot of danger across the way and some nice persons, but manages to get to his friend, the small boy that anticipated so much for Lassie's return.
Lassie was a real hit. The beautiful dog with the rich hair, the folded ears that stood up whenever Lassie heard of a danger apporaching, the faithful and good-tempered dog was loved by many people, so much that everyone wanted a Lassie dog (as they call them instead of the breed) in their home.
Lassie was great with kids, with other animals, it was a member of the family.
The hit of the first movie brought many more, such as the Son of Lassie and others. Mostly, though it was known by the series that was on from 1954-1973.
And from that series I got to know Lassie. It was one of the shows that the Greek public television channel showed -usually early in the afternoon- in the 1980s and we watched it all the family together. My father used to have a dog in his childhood and loved the spirit of Lassie, it kind reminded him his own dog.
From the opening scenes, sometimes he used to call : "Lassie! Come here!" and my brother and I used to laugh with him. (But he didn't like the New Lassie, cause as he said, the show wasn' t the same somehow)
And I continued the family tradition, watching with my nieces, when they were little, the animation of Lassie.
Everytime I meet a Collie Dog it reminds me of Lassie and all the afternoons I go to spend with my family watching Lassie. And it brings a smile to my face till now.
Happy memories!
This post was written in response to 
Thank you for reading!
*Author's note: I really don't want to use that word with animals. I used it only for the sake of explaining the plot.