It is unacceptable to demand sexual acts.
Cal was about to have sex with Ana, but he also wants oral sex.
Cal wants to get Ana to give him oral sex.
Cal asks Ana if it'd be okay if she gave him oral sex.
Cal tells Ana to get on her knees and start giving him oral.
Ana is more willing to give Cal oral and appreciates that he asked for her consent.
Ana feels like she is being raped and is not aroused anymore.