Fun fact the brain actually filters the smell out. When the smell of your noses internals changes, or your brain stops filtering it for whatever reason (common during illness), it tends to smell putrid. Often described as a smell of “decay”.
That’s not even because the smell is that bad. It’s just a mildly bad smell that happens to be right in your smell receptors.
Covid caused a funny phenomena with that too as it causes a heavy change in taste/smell perception.