When a strong virile man has a cock cage on possibly with a leash on at a couples fetish party. His strong woman is holding the leash. Like in a Stag/Vixen relationship.
The mental image is similar to how a rich person would show off their pet tiger. Instead a woman is showing off a large powerful man with a large cock. The implication is that if you are nice to the woman, she might let you pet her tiger/play with her mans cock. Tiger in a cage/Tiger on a leash
She has that tiger on a leash. She has that tiger in a cage.