The class and the bus shrink to their smallest ever in order to see molecules. In past episodes, they were shrunk where they could still be seen by the naked eye.
Wanda: (about Molly's hood ornament) What's it made out of?
Molly Cule: That's my little secret, Sugar.
Ralphie: Is is just me, or did she just call you 'Sugar?'
This is the first time Tim has a high-pitched voice. All other kid characters have high-pitched voices, as well.