Some thoughts:
Ueno-san has turned the classroom into a hermetically sealed bunker. I have suspected this, but now we see proof.
I was about to ask why Yamashita was cosplaying as a squid (not an octopus, the difference is obvious), but on second thought I probably don't want to know.
This chapter confused me, for some reason. Not sure why. A good
Ueno-san chapter is always bizarre, but they don't usually confuse me. I don't think it's a problem with the translation, though, so thank you for your hard work.
Also,
@Tcof Are you trying to say "ahoge" or "ahegao"?