I was thinking why in movies or shows aliens always just happen to have genitals that are compatible with humans. Sometimes it's not aliens but monsters or other such things. My point is that I used to think this was lazy writing or a plot hole, but then I thought about it. Any sexually reproducing animal tends to have the same genitals (sometimes a cloaca for the male instead of a penis but its about the same) the only difference is in the size, color, or exact shape of the unit and length of the act. Still I think it unlikely that aliens would have size compatibility, but nonetheless it's reasonable to think that similar genitals might evolve from any animal anywhere in the universe the reproduces the same. It's a fairly efficient model and very simple. So what does everyone think, would any theoretical aliens have compatible genitals with humans?