To have sex.
My grandpa used to tell me this history that when he was a young
lonely boy at the farm, he heard a legend that if you put your willy inside a goose, and then try to drown it while
making love to it, the goose's vajayjay start to contract and become's really tight, which feels really good and makes you release your swimmers faster. Later on this became an
euphemism for having sex among farmers.