why does the the animals call custard percival

The reference of percival has been taken from the stories about King Arthur and Camelot. In these stories, Percival is described as uneducated and although he wanted to be a Knight, he did not possess any heroic traits of a knight and was mocked at by everyone. Custard, the dragon was laughed at because although he was a dragon still he was always looking for a safe place.