Continuity mistake: During Christian and Ana's last Red Room scene together, there's a moment when Christian rubs, I'm assuming, some oil on Ana's body-more specifically her chest and breasts. When Christian enters her while she's on her side, there's no indication that the oil is still on her body, and Christian rubbed a lot on her. This is a continuous shot, so I doubt it could have dried up that quickly; it's also more noticeable when she's on her back and you can see the area(s) better.
Trivia: When Ana is telling Hannah, her new assistant, what she expects of her in the job, the dialogue is taken from the 1988 film "Working Girl," starring Dakota Johnson's mother, Melanie Griffith. Ana says, "I expect you to call me Ana. I don't expect you to fetch me coffee, unless you're getting some for yourself, and the rest, we'll just make up as we go along." In "Working Girl," Melanie Griffith says, "I expect you to call me Tess. I don't expect you to fetch me coffee unless you're getting some for yourself, and the rest we'll just make up as we go along."