Doug's Fat Cat / Doug and Patti P.I. - S3-E1
Other mistake: Doug's Fat Cat: After Stinky is revealed to be a mother, there is a shot of two of the kittens playing with each other. The two kittens keep turning into the opposite kitten repeatedly (you can tell because they keep flashing opposite colors), indicating that the animation is simply looped over and over. (00:11:14)
Doug's Fat Cat / Doug and Patti P.I. - S3-E1
Other mistake: Doug's Fat Cat: When Doug imagines himself reporting Stinky on the phone, when Stinky is chasing Porkchop, her tail is layered over the wall in front of her. (00:02:15)