What is the independent variable in this experiment? (Look at the photo)

what if one day you woke up and your nipples were completely gone
like no scars or anything, just flat skin
and then once you leave your room you find out your dad died last night
and then several days later, you find out that for your entire life your dad had been sneaking into your room while you slept
and sucking on your chest to make to gigantic hickeys where your nipples should be
because you were born without them
not for any sexual reason, just so you would fit in 6+9=hash’s forgive washing Tom

It would be

Hope the image of the frequency formula