Every single time a truck drives by (garbage truck, mail truck, grocery delivery, any rumbly truck or suv), Sunny gets fixated on it and stares at it with her alert, ears forward pose. As soon as the vehicle moves Sunny pounces into action and tries to chase after it as she makes these weird high-pitched yelping noises (not quite barks, more like pug screams?). It can be really frustrating but also entertaining. Rosy doesn't care about vehicles at all. I like to imagine that this is what Sunny sees when a truck drives by.