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 sweeps the floor litter into the tiger-skin rug, the Pink Panther ejects the litter and you can see that the janitor's sweeping brush and litter are by the rug when he runs off to fetch a gun. But when the janitor returns with a gun, the litter and sweeping brush have disappeared.