"Mamma! Papa! Mamma!" came the voice again.
"It—it's kind of funny," whispered Flossie to Freddie. "Don't you think it's kind of funny, Freddie?"
"Yes, but I know what makes it."
"What?"
"It's being in this cave. You know how we used to holler at the hill, when we went to the country—'member that?"
"Yep," answered Flossie.
"An' how our voices used to come back an' sort of hit us in the face?" went on her brother.
"Yep."
"Well, that was an echo," said Freddie, "an' that's what makes it sound so queer here. It's an echo."
"Oh," said Flossie. She had not thought of that.