I think it's because there's no need for it with humans.

[That was a mechanism designed to ... Basically force the female party to take the cum, right? To ensure the whole knocking up idea. Which is funny because a lot of human guys have to worry about trying to pull out in time. And upon being reminded of the swimming escapade she grins.]

Oh, man, that was such a great day! [She missed that bikini.]

Freezing me all over? [Or just a certain part? Either way, he's gone ahead and grabbed at her so she does the same, sneaking her fingers over his cock so that she can pump it lazily. This isn't her ultimate goal, but she's trying to take it a little slowly.]