Vagina gapes too. A gape is just women's body adjusting to accomodate cock.
Gape does not mean cock is not under pressure from anus. You will never see gape bigger than the size of cock because gape is just momentarily opening and a quick after impression of cock. Anal gape starts closing soon as cock is pulled out. When it is in it wants to close and so it exerts pressure (both rectum and anus) which is a tight sensation for men.
Hope that answers your question.

