Not necessarily jokes, but people's fatness is pretty much always pointed out as something that makes them unattractive, and several characters that we are meant to dislike are fat, while no 'good' characters are
A woman's journal entry is mistaken for having called Down's syndrome an 'awful sickness', though she is actually referring to the non-specified mental instability of her own son
The book is split into two halves, one a book-within-a-book section, and one with the editor of said book. The editor's sections occasionally address the audience as a general you; the editor is aware that she is writing to an audience, and is also aware that she is actively involved in a whodunnit plot, which she comments on frequently