This phrase is commonly used when describing a skip holed whore who doesn't wash properly. The smell, when she opens her legs can make a man faint if he goes down on her. Even when wearing jeans she is often told to 'CLOSE YOUR LEGS LOVE!'.
This phrase can be used in many circumstances, but this is the most common.
Person 1: Did you fuck Steph last night?
Person 2: Yeah mate, I fucked that whore good, but her Salmon Flaps nearly ate me whole. Boy was she smelly! Like a Salmon.