Sisters

We have a Cobb family picture hanging up at our house. Daniel pointed two people out to me. 

D: They look exactly like each other except one of them is nana and one of them is not. 

Me: Do you know who that is?

D: Who?

Me: That's nana's sister, Susan. 

D: Cool, twins!

Me: They're not twins bud. 

D: They are twins if they look exactly alike. 

Me: That's not what makes them twins. They're twins if they grow in their moms belly at the same time. 

D: Oh.