Casey tramples her slave's cock with blue vinyl very high pointy heels.

You can hear the shoes crunch and squeak as she walks, gets on the cockbox and plays around with her slave.

You can see her do her thing from a POV as well as side view. If you watch closely, you can even see the cockbox bend under her pressure.

It's to no surprise her slave can't hold it in for too long at all. The end is a relief, the sore balls stick around for a while as she steps on his load.