It's not the poop. Some species of geese and swans can be really aggressive. Chinese geese, particularly. They're big, people often have them on farms. They'll chase you around the fields, squawking, flapping their wings, and trying to peck, bite, and kick you. To a kid, that is a horrifying experience.
Roosters also flog people, but compared to being flogged by a goose or a swan? It's scary, but not as scary. Though, their claws can leave some nasty cuts on your legs.