Corrected entry: After Phoebe puts hinges on her cast and Helga and Phoebe are in the library. After Phoebe gets away from Helga and hides within the library shelves, she opens her cast and starts scratching her leg. When Arnold sees Phoebe he says to her, " I just saw you open and close your cast." Yet Phoebe never closes her cast.
Corrected entry: Towards the end of "Bio Square," Arnold and Helga manage to escape drowning in the titular Square (from a haywire sink leak) by jumping onto her inflatable mattress. The two ants from an experiment by Arnold manage to escape, too, by jumping off a table and onto a floating, half-eaten potato. However, at the end of the episode, when Arnold and Helga are describing their adventure before their science class, Arnold says that the ants "climbed onto the leaf." Knowing how sharp Arnold is, it's unlikely that he mistook the potato for a leaf. This is a simple script error.