Me: Are you going out to feed the birds?
Daughter (seven): No, the chickens.
Me: Chickens are birds.
Daughter: (derisively) No they’re not!
Me: So why aren’t they birds? They have feathers and beaks.
Daughter: They can’t fly.
Me: Penguins can’t fly, and they’re birds.
Daughter: (confidently) No they’re not.
UPDATE: The nonsensicality of this argument was exposed a few days later.