What is a mouse breather?

I suppose there might be some obscure sect that inhales rodents, in the way that there are snake handlers. Or an odd addiction to sniffing the critters. But I've seen neither hide nor hair of such practices.

“He's such a mouth breather. Why do you hang with him?”

Oh dear. I'm picturing tiny little breath masks for rodents. Maybe they're working in a hospital, or seated on a plane where the masks drop out of the ceiling. Doing CPR on a fellow murid who got away from the cat just in time.

How should one handle a situation where they suspect their partner of cheating, but their partner denies it and claims it is all in their head?

Cute as the notion is, I think the phrase you're looking for is mouth breather. As in someone who breathes with their mouth open. There are a number of medical conditions that can cause chronic mouth breathing, when the nasal passages are blocked. But calling someone a mouth breather outside of a medical context usually means you think they're slow or stupid.

And I have seen the idea used in a couple of murder mysteries, where a victim was tied up and their mouth taped closed, leading to unintended death by suffocation. It lives in the same story space as the rare thin- skulled individual, where a tap that would make an ordinary person unconscious becomes a death sentence.

And the adorable little mouse breathers now have a space in my imaginative visual vortex. They're just so cute.

How did a computer scientist such as Geoffrey Hinton manage to win a Nobel Prize in physics when computer science already has its own Nobel Prize equivalent in the Turing Awards?