I'm not sure that bolt is her tooth or uvula.

I think the bolt is her tooth for two reasons (according to my analysis). First, the alignment of the bolt with the teeth supports the fact that the bolt a tooth, if the bolt was the uvula, I would expect it to be a further in depth, like behind the teeth and the shade would be bit darker. Secondly in theory, (even if this is anime) in reality, could you really french kiss someone, and stick your tongue all the way back to their uvula? That's just my opinion.

Nano is in pain... >_>

Hakase, why would you put a bad teeth into Nano?

Nano has accepted Mai's kind offer to reinstall her loose bolt (or was blackmailed, see Episode 15).

SdCdS said:
Hakase, why would you put a bad teeth into Nano?

> Nichijou 34 (episode 08)

Talk about turning the screw.

I'm confused who is being stimulated here. I know Nano's face is nearly red but that would be more from the pain I'd imagine.

This image is confusing, but after reading the artist's comments, I think I get it.
I'll paraphrase with my interpretation of events.

The word mushiba (cavity) printed above the tooth is misleading. Rather than a cavity itself, I think this is supposed to represent Nano's cavity feature (proposed by the Professor in episode 8). According to the artist, the way it would work is, the acid produced by the bacteria in Nano's mouth would rust the tooth, causing pain. So this isn't a decayed tooth itself, just a tooth capable of decay (unlike the rest of her teeth).

In Episode 15, they're all trying to out Nano as a robot. After Mai sees Nano lose one of her teeth (the screw that comes out of her mouth) she decides to investigate further, and starts feeling around inside Nano's mouth (with her tongue) for anything suspicious.

Nano is red and flustered not because she's in pain (or even pleasure necessarily), but because she's worried Mai may have discovered her secret (and also because she's being French kissed).

Gaketsu said:
(Sh- She's feeling it!? She's feeling one of my robot parts!? ...Ahh, she's going to find out... she's... ah... haah...)

In reality, Mai is a secret minion of Kana, who wants to capture Nano. She's now entering a secret obedience code via the Morse interface (the tooth button, designed for the case, when an older Preofessor Sakamoto would have to subdue Nano vai seduction).