The Big Tick - S2-E2
Factual error: When Gwen and Grandpa Max use the shell plates from the tick to ward off it's corrosive secretions, their fingers should have been eaten away since they were grabbing the rims of the plates when the acid came raining down.
The Arwin That Came To Dinner - S3-E8
Factual error: In Season 3, "The Arwin That Came To Dinner," in the scene where Arwin is licking his plate clean (that supposedly had food on it), notice that when he does this you can hear that high pitched waxy sound. Oddly enough, if you get a clean plate straight from the dishwasher and rub skin against it, you can hear that same sound. Meaning that there was never any food on it.