This article is a valuable read for anyone involved in supporting any survivor of serious trauma. Essentially, cops (and others) expect the survivor to be crying and freaking out. This article warns us of the danger of using survivors' outward expression to judge whether or not their story is believable.
Fortunately for most of us, we don't often deal with people who've just experienced horrific trauma. Most of us have a poor understanding of survivors' reactions to terrible and rare events. This article explains how survivors commonly have unexpected emotional expression when they tell their stories. They may have a flat affect or crack jokes. They might not seem to be taking themselves seriously.
The important lesson here is about how people supporting survivors can do better. We reject the cop-centric focus of this article. There are many reasons that cops have incentive to disbelieve rape victims: they are more likely to have committed violence against women themselves, they wish to preserve their own power, or they simply may be avoiding more paperwork, and all the other reasons that anyone else disbelieves rape victims.
Finally, to reject a survivor's story is to assume the survivor is a liar or delusional. Believe survivors.