that you choose to do something else, torture him with the sight of her being unfucked—
One day put them in the same cell together. (You know what’s going to happen.) Open the door the next day, see him frantically driving his caged cock into her groin, trying desperately to hump her, have his way with her, relieve himself of that heat, cum, using her body—
As punishment you make him force his mother to cum five times with his hands, whilst he’s not allowed to touch himself at all. Spraying pussy juice all over his arm and chest, crying out in terror-ridden pleasure—then she starts moving her hips and using him just as you use her…
When she’s done, unconscious after cumming eight times on his hand (the slut), you take her limp, ragged body and slowly plunge your cock into her