In 'Hey Arnold!', what shape is Arnold's head often compared to?

In 'A Charlie Brown Christmas', what kind of Christmas tree does Charlie Brown choose? In 'Dexter's Laboratory', what is the name of Dexter's annoying sister? What are the names of 'The Powerpuff Girls'? In 'Gravity Falls', in which state is the town of Gravity Falls located? In 'Rugrats', who is the bossy three-year-old cousin? In 'Arthur', what kind of animal is Arthur Read? In 'Doug', what is the name of Doug's dog? In 'Blue's Clues', what kind of animal is Blue?