Biology Lessons with a 4.5 Year Old

Tonight when getting ready for bed, Abigail asked me out of the blue:
"Mama?  Where did Dinosaur [her imaginary friend] come from?  Did he grow in someone's belly?"

My little mammal.

The following conversation ensued:

me:  "No, sweetie.  Only mammals grow in bellies to be born.  Dinosaur is a reptile.  He grew in an egg, like a chicken does."

Abigail:  "Oh."  [thoughtful face, incorporating this into her brain]

me:  "You know, you grew in someone's belly before you were born, since you are a mammal."

Abigail: [giggling] "MAMA!!  I am not a mammal.  Mammals are animals!!  I am not an animal!!"

me:  [ruffing her hair] "You are furry.  And you love milk.  You are a mammal AND an animal."

Abigail: [giggling harder] "Mama!! Huh uh!"

me:  "Well, what else would you be?  Are you a plant?"

Abigail: "No.  I am not a plant!" [I can see the wheels
turning again]

me:  "Well, are you a rock then?  Or are you an animal and a mammal?"
Abigail: "I'm an animal!!"