1 Ishmael: I mean, do you have the right... you know, anatomy... to breed with human women?
2 Martian 1: We're males! Of course we do!
2 ishmael: Right! Okay! Yes! Sorry to ask.
3 Martian 1: We are extremely well endowed!
3 Ishmael: I don't need to see for myself!
4 Martian 1: These claws are perfect for nipping off the young buds and planting them in nutrient gel.

Some half-human hybrids are at least moderately reasonable in that the reproductive systems and methods are similar - think mammals interbreeding with mammals.

Some are less reasonable because although the principles are similar, there are some distinct differences in how the process works that make things tricky to explain - think mammals interbreeding with birds, or even fish.

Some are much less reasonable because of basic incompatibilities in how the whole process works - think mammals interbreeding with insects or other arthropods.

Some are even more outlandish and absurd because things are getting really divergent - think mammals interbreeding with plants.

And then there are the really extreme cases, where even imagining how it would work is brain-bending - think mammals interbreeding with fungi.