Continuity mistake: Charlie Brown's Christmas tree is never the same. When we first see it, it has three branches. Later, when he's carrying it, it has four branches. Then, when he tries to decorate it and it flops over, it has six branches.
Continuity mistake: When the janitor is sweeping litter, he stops when he hears the Pink Panther driving the car and there is some litter in front of him. But when we return to the janitor later on, the litter has disappeared.