About 20 minutes into the walk, they pass a park and see two bunnies mating. The woman says "how does the male bunny know that the female bunny is ready for sex?" The man says "it's natural, the male can smell it".
The couple continues to walk for another 20 minutes and they pass a forest where they see two deer mating. The woman says, "how does the buck know that the doe is ready for sex?" The man says "it's natural, he can smell it".
They walk for another 20 minutes where they pass a field of cattle and see two of the cattle mating. The woman says "how does the bull know that the cow is ready for sex?" The man says, "again, it's natural. He can smell it".
They finish their walk and the woman drops the man off at his place. She kisses him goodbye and says, "you should get tested for COVID-19". The man said "what makes you say that? We're both vaccinated, right?" The woman says "you may have a breakthrough infection because your sense of smell is clearly not working."