There's a great NPR piece about Vonnegut's daughter - who read and gave feedback on Slaughterhouse-Five.
N VONNEGUT: And I have to say, when I was reading, he would be in the next room. If I laughed, he'd come running in because...
INSKEEP: (Laughter).
N VONNEGUT: ...That is what mattered (laughter).
INSKEEP: He'd want to know which joke landed.
N VONNEGUT: Absolutely, every time.