[digitalscribe]

This was an interesting discussion when I read about it long ago.

I don't think it's obvious that Marilyn's interpretation is the correct one. Two possible interpretations could be equally valid.

In law we have the "rule of the last antecedent" that says descriptive clauses modify the nearest antecedent noun.

Under this interpretation "which has a goat" modifies the exemplary door "say #3". Same as saying host opens a door, for example door #3 containing a goat. It could have been say door #2 containing a car.

Marilyn's interpretation is that "which has a goat" modifies "host opens another door." Same as saying the door opened by the host always has a goat.

Language is inherently ambiguous. I don't think either interpretation is unreasonable...