Literally a half hour after the "who let the dogs out" comment:
Audrey, downstairs, is eating her cereal (with milk this time). Gracie toots again (I guess she has gas).
Audrey to Daddy, smiling: "Did someone step on a duck?"
I don't know where she got "who let the dogs out", but she probably heard me say this once. Regardless, she obviously has the potty humor thing down pat.