The second half of the episode shows a wordplay on wisdom teeth (alternatively read as "teeth which parents don't know about") and during the entire gag, voice actors change around for every character.
What's the joke in that?
The second half of the episode shows a wordplay on wisdom teeth (alternatively read as "teeth which parents don't know about") and during the entire gag, voice actors change around for every character.
What's the joke in that?
The original manga chapter this was based on (ep. 97) was the first chapter published after the announcement of the first season of Sayonara Zetsubou Sensei, along with the staff and cast working on it. In this episode, whenever a character appeared, a subtitle with the character name and voice actor was also displayed, to drill the information into the heads of the readers (which at the time everyone thought "I know you're happy about the anime. I get it already.").
The anime studio took that joke and played it reverse, since it was a joke that only made sense in textual form (and we've listened to their voices for 1.5 seasons, so it would just sound like stating the obvious).
So basically it's a twist on a joke that only worked in the manga, which was published right after the announcement of the first season.