Dou Dou is fixated on cats, cars in a distance (but not ones passing nearby), and newly added to the list is garbage trucks. If he can't (and he can not) have a cat, car on the horizon, or garbage truck, then he finds there is nothing better than his nylabone... or anything else made of hard plastic, such as his food scoop, food bowl, or anything with plastic handles.
Some things he does not care about are gun shots, thunder, howling coyotes, or sirens.