Olfactory fatigue. It's where your nose senses can not smell certain smells any longer because due to being within it for so long. Ever been in someone's house and it stinks? To them it may not because they are so use to it. I've been in people's house where their cat stinks the place up, but they can hardly smell it at all. That's a shame. It's like making popcorn. The whole house smells like it, but after a while you don't smell it that much anymore. Then if you go outside for a few minutes and come back in, you smell just as strong again! Some people just don't know they stink!

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