Well, you see, first you visit your grandmother and notice she looks a bit different.
"Grandma, what big eyes you have!"
"All the better to see you with, my dear."
"Grandma, what big ears you have!"
"All the better to hear you with, my dear."
"Grandma, what a big p**is you have!"
"All the better to impregnate you with, my dear!"
And then she does.