Minor spoiler alert: IV pg 47 "Zonk"

[Joe Allonby]

"What's behind the door where Carol is standing..." refers to Carol
Maryl - Monte Hall's leggy but mute sidekick on pioneering game show
"Let's Make a Deal" which exploited people's willingness to humiliate
themselves on television through displays of greed and stupidity. A
zonk was a gag prize: you lose.

See also Cheech and Chong's parody "Let's Make a Dope Deal".