This is more a curiosity question than anything, not majorly important.
Recently, when spending time with friends, there was a particularly bad smell in the area that everyone was complaining about, I was unaffected as I had closed off my nasal cavity. Everyone was surprised and fascinated by this, I had always thought that everyone could do the same, but after discussion with friends and family, it appears I'm the only one we know who can do this.
The passageway at the back of my throat that leads up to my nasal cavity is something I can voluntarily close, I've always been able to do this for as long as I can remember, it's always been useful when bad smells are around, or if I have to take some particularly bad tasting medicine.
Is this a gene I have that allows me to do this, like the tongue-rolling gene? Or is this something that anyone can do if they've learned?