When, after having anal sex, the person being sodomized sucks the sperm and their own feces off the penis of the person doing the sodomizing.
The term originates from the (alleged) saltiness of ejaculate combined with the chunky brown consistency of feces.
Bob: So you think she loves you?
Jack: I gave her a salty snickers last night and she loved it. She's mine.
Bob: Better run. She'll be wanting to get married next.