Pet in heat

I don't believe I have any pictures handy, but I can tell you they get hearts floating around them, so you can tell they are in 'need'.

They bark and howl and hearts surround their head as they howl. (i don't tend to adopt cats as I'm allergic to them irl I believe they meow in heat similar to howling)

It's annoying. It's virtually nonstop. Even if they can't have pups or kittens they still go into "heat" mode.

That said, some will run away during heat. Dog or cat hangouts are good places to ask your pet to mate with another pet if there isn't an option in the home.

It sounds like somebody needs to make a mod or something to block that if it's not possible for them to have a litter (altered). That's the way it works IRL!!

It is possible. They do have hearts floating around them. Prevent this by getting 'em spayed or neutered. If the Sim doesn't do anything to prevent the mating, the cat or dog may get unexpected litter, from breeding. You can switch the ability in CAS, with the three dots, from "Natural"
to Fixed. If you use a trait (and hidden trait viewer), there is either a "Unspayed/Unneutered" trait, or "Neutered/Spayed" trait. Now if you have the Unspayed or Unneutered traits in this viewer on your pet, replace it with "spayed/Neutered" if you don't want heat or litter.