Not including the slurring for the yukkuri, I think this is:
Marisa on the right: Yu! Welcome back, mister! Reimu: Welc... (starting to say "welcome back") Marisa on the left: Yupii! Mister, Marisa's stomach is hungry! Human: I'm back.
I mean, sure, this Reimu's a little shit and deserved punishment, but how did he not notice a yukkuri in his front pocket?
Yeah, it defies credibility that he was unaware of a yukkuri in his breast pocket. If he wasn't carrying it on purpose (for what possible reason?), he must be some kind of idiot.
As a human being of course I am rooting for the villagers, but this yukkuri demonstrates a very human level of ingenuity. Lacking in strength and natural weapons, it instead uses intelligence to make up for its physical inferiority.
My interpretation of this picture is different from HankySpank/Skribulous's take on it. I don't think that this picture is supposed to show an evolution of the yukkuri's attitude from grateful to inconsiderate. I think the point is to show the gap between the yukkuri's words and its intentions, and how its poor ability to express itself makes its intentions seem more rage-inducing.
Not that the offer in the last panel wouldn't be annoying regardless of the intention behind it, but "Hey, my poop is actually nice, I bet Mister would like it" -- especially considering that its poop ~really is~ bean baste, and humans have been shown in other panels deliberately eating it -- comes across better (misguided but considerate) than an arrogant-sounding "eat my shit."