I am always careful when reloading rounds: Read everything twice, no distractions, all that thing. I also always don't eat or drink near where I'm reloading.
Except for once last year when I was making up a batch of .303 British. I was pouring powder for about 20 rounds while eating one of Stouffer's tasty Crustini Chicken Broccoli and Cheese. I thought that something fell from it while I was pouring powder but I couldn't find anything on the table. Didn't occur to me to check the small container of powder that I had on the table.
One week later I'm testing those very rounds at the range when I hear a small pop. After giving it the standard 1 minute for hang fire I eject the case out of my Lee Enfield. Primer had gone off but when I check the inside of the case there's an odd mess of greenish powder and some goop. Turns out I found the small piece of food that had fallen into the powder. It also turned out that the bullet travelled about four inches into the barrel and wasn't going to come back out. I managed to get it out later with a wooden dowel, a hammer and some pounding.
I've never eaten or drank near the reloading table again.