Some would say quite similar to the asshole, the anal sphincter is like a little drawstring that loosens and tightens up your asshole when things are coming in and out of it.
My grandma has shit constantly flowing out of her asshole, she must have a problem with her anal sphincter.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.