Iirc 8 key triggers an ejaculation animation, and there's an inflation slider you might find needs tweaked in the settings.
Viewing post in Wicked Island Demo 0.8.5.2 comments
That one is just effects that you can trigger on your character at any time. Even when not doing sex. (So it's not a cum butten).
The slider in the settings was set to 100%, and yet nothing happens during sex. And the the only time it does is when you end the sex, but that's more like a aftermath then an animation like some would had hoped it do instead.