Jessie Spano says that she found out that her ancestors were slave-traders. "Spano" is an Italian surname, and the Italians were not involved in slave trading nor involved in slavery in any way. Jesse could have non-Italian ancestors who were involved in slave trading. Alternatively, one or more of Jessie's Italian ancestors could have been pressed or swindled into service on a slaver.
Zack enters The Max after running in a track meet. He is still wearing his track uniform and sweats, so he hasn't showered yet, but he appears perfectly clean, with clean hair and no perspiration.
When Screech uses the toy tomahawk to slice Mrs. Wentworth's apple in half during Zack's presentation, Screech whacks it hard on the top and it falls into two perfectly even, pre-cut halves.
While giving his presentation, Screech says "Buonasera," then tells everyone that it means "good afternoon" in Italian. It actually means "good evening" in Italian.