Here's a chemical puzzle for you: all of us who have worked in an organic chemistry lab can agree, I think, that pyridine reeks to the skies. My descriptive powers aren't up to conveying its smell, because it's really unique - foul, penetrating, and like nothing else but pyridine.
And we'll have no trouble agreeing that thiophenol is a stinker, too. It's one of the prototype stinkers, actually, since it's the main smell of burning rubber. (Imagine that aroma concentrated and ready for use in a bottle, and you've got thiophenol.) Now, what if we take those two structures and combine them?
You'd figure that, say, 2-mercaptopyridine would be impossible to take. But it has no smell whatsoever. (Some of you may be ready to e-mail me about how this compound isn't completely an SH, that it has some thioamide character. But before you do that, recall that thioamides are unbearable, too.) No, this seems to be a case of smells cancelling out at our nasal receptors. For whatever reason, a molecule with the combination of a pyridine nitrogen and an aromatic thiol doesn't set off our sensors.
And that's a good thing, considering what it would be like. Now, I guess you could make a one-molar solution of thiophenol in pyridine, and that would do the trick. I'll bet nothing would cancel out then! Fortunately, I've never come across that reagent combination, and if I ever do, I'll find something else that urgently needs my attention. . .