Boo!

The girls know about ghosts, at least how ghosts appear in their children's books.  Every once in a while, they will walk around with a towel or blanket over their heads while saying "Wooooooooh!"

Elvin was upstairs and came into the master bedroom to this sight.  The girls were whispering something to each other underneath the sheets.

Then suddenly...

"Boo!" the girls yelled.

After Elvin looked sufficiently spooked, Eliana asked: "Did you know we were here on the bed under the sheet?"