Nonhumans Lack Attributes/Analysis

Stock Explanations for Addressing This Subject
It's rare to see anyone actually address the subject onscreen, but if the matter does come up, expect to see one of these stock explanations:
 * The genitalia of some creatures (e.g., reptiles, amphibians, fish, monotreme mammals, and birds) just aren't externally visible to begin with.
 * Even when they are, these "attributes" might be so alien that we humans wouldn't recognize them as such anyway.
 * Some creatures have external genitalia, but they are not conspicuous (e.g., cats, rabbits, guinea pigs, and beavers) and are at least somewhat easy to avoid noticing in Real Life.
 * Some creatures (e.g., sponges, even frogs and toads) just don't have any genitals to begin with. For this explanation, please just list aversions as animals correctly lacking genitals are People Sit on Chairs.
 * Some forms of life are so alien that they may not even need to have such anatomy in the first place.
 * The details are logically present, but are obscured beneath a layer of body fur or other Bizarre Alien Biology.

The last explanation is probably the most common assumption, even though it's not true to Real Life observation. With many mammals, the body pelage (covering of fur or hair) is actually thinner around the genital area (to avoid getting it soiled when nature calls). The human is an exception to his rule as the hair around the genitals (or pubic hair) is thicker, but it doesn't hide male human genitalia. Also many mammals don't have a thick enough coat to adequately conceal their genitalia in the first place. The male pig, for example, has a rather prominent pair of features on its underside that are hard to avoid noticing in Real Life, even though the fictional male pig never has them.