Is smell a good way to tell if food is safe?

Nick - It can be, but I think there's another important point there as well. You can often throw food away before the sell by date - just because it's got a date on it, it doesn't necessarily mean it's safe up until that point if hasn't been stored properly. But yes, smell can be an indicator that the spoilage process is starting, though it's one of several things that you might use.