Would have been best to get up & actually see what the snake was doing. They don't typically digest their food in 3-4 days, which is how long after feeding you said this usually happens, but eating a meal might be pushing out some gas in the snake's GI tract about that time. I assume you're sure the snake has never regurgitated any meals? Your nose would likely not miss it if the snake did regurgitate so it was probably just passing gas.