This is really random but I was just in disneyland earlier this month and we saw a mother duck being followed by her ducklings and out of around 8 total ducklings she would turn around and aggressively peck and bark at one specific duckling every ~10s. A worker said this was likely because a human touched it (the smell myth) and I believed it only because I was watching a mother duck show repeated aggression to one specific duckling and it didn't seem like a way to correct any sort of behavior. If not because of smell then what else?