I was putting together a blackberry jam sandwich this morning with a knife I grabbed from the counter. It was only halfway through making the sandwich that I realised there had been a yellow residue on the knife. That worried me... but then I remembered it wasn't any mystery substance, but rather some hot mustard from last night, so I continued.
It wasn't until I finished making the sandwich that I realised: it's probably not right to be so nonchalant when making a jam-and-mustard sandwich. It wasn't that bad -- kind of like a jelly doughnut that makes your sinuses run -- but still.