Dogs do not howl at sirens in Vietnam

It just hit me today, when I was upstairs I heard an ambulance go by my house on the canal.  For some reason a memory from my youth back home in Centralia, Washington, popped into my mind.  Everytime the fire trucks, police cars or ambulance turned on their sirens, the dogs, I mean all the dogs, would howl at them.

In Saigon, there are dogs everywhere, at least one per house.  My old dog, Lucky, used to bark at them throughout the night on the terrace.  Yet not a single dog howls at the sirens, and there are many  here.

Has anybody ever noticed that?