The sperm left over on the womens body
after the male
ejaculates onto the her, then the female cleans
it off and the residue left over is the sperm slug.
sally went down on big johnny and as he tells
her to get off of him, he ejaculates onto her so she goes
to the bathroom
to clean off. As she gets ready for round two big johnny tells
her " little
sally you have sperm slugs all over"