The sentence just doesn’t sound right for some reason. Maybe because it’s using both him and his in a short span.
It’s a cartoon so I can see where you couldn’t really rephrase it and still get a joke out of it. And it probably would be better to rewrite the sentence, if it were in a book or something, but I was just wondering about the grammar aspect to it
But I agree that these sentences are grammatically correct. We’re obviously missing the information and context that would make them sensible (or not), but there’s no problem with the grammar.
Maybe a period at the end, too. Otherwise, I see no issue. Having separate sentences is not even a problem: you could have a colon or semicolon separating the two and it would still be okay.
I was also going to recommend adding a period after “his”, but I remembered that in American comic book style, the final sentence in a word balloon is left without a period, although question marks and exclamation marks are used.