The Lion and the Mouse was a fable that Ryan Sinclair's gran, Grace, used to tell him.
In the fable, the lion was planning to eat the mouse, but the mouse persuaded him that there would be no honour in that. After the lion let the mouse go, he was captured by hunters. The mouse then saved the lion by chewing through the hunters' nets.
Ryan could not remember whether the lion then ate the mouse or killed the hunters. (PROSE: The Good Doctor)