on the first season episode " the voice of tinker jones" as the kids are leaving school for the day and on their way to tinker jones keep your eye on willie as he is running he suddenly trips and nearly cleans himself up on a tree stump if he had struck it he could have had a serious head injury!

Notice that when the bell is first rung, it has an offkey,melancholy tone to it (more like a Russian church bell- and somewhat apt as Tinker Jones used whatever scraps and silverware the kids managed to sneak into the mix)... but every time thereafter in the series, it has a clearer and more conventional tone!