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 lion jumps into the basement while chasing the Pink Panther, the doors of the basement are initially flat but in the next shot they are slightly raised.