As the title says, just wondering if there is a difference in what animals like dogs and cats perceive as good smell vis a vis humans. Example : Smell of some flowers - great . Fart smells - bad.
TL; DR Mostly no.
On a molecular basis, cats' and dogs' noses look quite similar to ours. Most of what we know about smell comes from studies on non-human mammals, and is supposed to apply to humans too. So, big similarity, but...
- Cats and dogs distinguish far more kinds of than humans. It's likely they know more kinds of bad smells and good smells, possibly including from things that we think lack odour.
- Many animals also have a working vomeronasal organ, that is, a sensing organ similar to the olfactory mucosa we use for sensing common smells. The vomeronasal organ detects pheromones, the smell-like signals used for communication between animals. We, humans, are at least deficient, if not completely unable to use the vomeronasal organ and pheromone signals. It is debatable whether animals conflate regular smells with pheromones. Pheromones are very efficient in conveying information about potential sexual partners, rivals, and so on. So these are a completely different set of bad and good smells, available only to animals. That is, if we can call those sensations smells, a big if.
- On the other hand, humans evaluate smells culturally. Some people learn to enjoy offensive smells that people from other cultures carry on disliking. Since dogs have limited ability to manipulate smells and to convey information to another dog, I doubt they can form these cultural constructs of smell. We sense sensuality in a perfume; the dog senses a bunch of pungent flowers, neither good, nor bad.