Thionyl chloride is one of the classics of organic synthesis - it is a robust reagent for converting carboxylic acids into acid chlorides.

I think it smells unpleasantly like buttered popcorn (mutiple people have told me I'm crazy for thinking this, but I insist it's there). There is a definite sulfur note, of course. It's a bit like tosyl chloride (see also Derek Lowe).

One hard thing to explain to someone who hasn't ever smelled sulfur compounds in any real quantity is the hangtime they have - you can get whiffs of it hours after leaving the lab. Additionally, they can pervert your sense of smell and taste (often reversibly). I once had a labmate who was a little sloppy with some 1,2-ethanedithiol. I wasn't working with it at all, but he got some in our drawer with rubber stoppers and some small glassware.

We smell these things in high dilution - occasionally someone's sloppy as above and there's the odd drop, sometimes you get a whiff between the fume hood and the rotavap. It's not like we're sticking our noses in bottles.

Back to the taste perversion, though. After getting whiffs of the ethanedithiol (which get progressively worse over time) for a week or two, I had a really good steak, along with some garlic mashed potatoes. Nothing tasted right! Somehow one nasty sulfur compound had ruined me for the tasty ones. Fortunately, this abated shortly after I left the lab (this was a short, 2-3 month stint) and was around slightly more careful colleagues.

I'm pretty careful with chemicals - especially the nasties. This is something you really have to pick up on your own. One of my big problems with chemical education is organic synthesis lab, something lots of careless 19- and 20-year-old sophomores do in college. You're given a list of procedures to perform for the day, and you're evaluated both on your ability to complete them all and how well you do them. Thanks to the size of the lab, how much you get at the end (your "yield") is usually used as a proxy for your skill. The combination of minimal time, minimal supervision (20, or even 10, novice chemists, is too many for one TA who is likely to only have a few years under her belt as well), and inexperience (with brand-new reagents of a toxicity previously unencountered in general chemistry) tends to lead to some unfortunate shortcuts.

It's a problem, because organic lab is indispensable to becoming a decent chemist. You learn so much if you pay attention (perhaps most importantly, whether you have "the hands" and should continue in bench science). Hopefully, if you get to the point where you're doing this 8 hours a day, you get it sorted out in a few months. If you're in graduate school and your technique involves some potentially risky maneuvers for the sake of yield, take some more care. Your liver (and sundry other squishy bits) will thank you a few years down the road.