I didn't really understand until today while helping out in Max's class where Max would get a question like he asked me. They are discussing mammals and nocturnal animals and all sorts of things like that. Is a bat nocturnal? Yes. Is it a mammal? Yes. Is an owl nocturnal. Yes. Is it a mammal? No. How do we know? It lays eggs.
Max: "Mom, did Miss Jennie Jo lay her baby yet?"
Max: "You know! Did she lay her baby? Will it be at Gavin's birthday party?"
Mom: "No Miss Jennie Jo hasn't HAD her baby yet, it won't be at the party!"
Apparently Miss Jennie Jo is not a mammal.... I wonder if she is nocturnal!