It smells like sulfur + burnt rice crackers to me... It's actually not that dangerous of a compound - I've spilled it on myself gloveless and it's not a big deal.

Also a bit of a possibly overpedantic note - you can run gels without reducing the disulfide bonds, but typically those proteins will run through the gel faster, not slower because of a more compact form. Because not all proteins have disulfides, if you reduce them first, it creates a predictable relationship between the protein size and the migration velocity, which is the desirable property, not speed.