Joke, oh so funny

This morning Breana and Juliet were in the back seat whispering and whatnot and then they started laughing.

I ask them what so funny

Juliet says "listen to my joke"

" I wish we had six fingers on each hand, cause then we would have two fumbs (she says the 'th' on all the other 'th' words, except for thumbs)"

she pauses for a second and you can see all three girls poised to laugh at the very second I understood the joke....which I was not

so Juliet continues "Get it?..... two fumbs!!! HAHAHAA"

All three girls bust up laughing, after they calm down they look at me in the mirror and I say "i'm sorry I just don't get it"

Juliet rolls her eyes and says "oh mom" and looks at her sisters like I'll never understand them.

I guess I'm just to old.... :)