It must be a duck

The old saying goes that if it walks like a duck and quacks like a duck, it must be a duck.

My Biscuit baby showed us a little logic of his own.

When he saw seagulls flying, he pointed and said, "Bird. Bird." (Of course, it sounded more like "Buhd. Buhd.")

But when he saw sea gulls on the beach in the edge of the water, they were ducks.

According to him, birds + sky = birds, but birds + water = ducks, even if they're the very same birds.

Makes sense to me.