Once I bought a big bag of pumpkin seeds. I stashed it in the cupboard for about a month, then came back to it. I put some in a bowl and started eating it. A few minutes later, when I actually bothered to look at it for the first time, I noticed some white cotton-like stuff on some of the seeds. I went to look into the bag to see if there was more of it. Then I saw them... lots of little moth caterpillars crawling all over the inside of the bag, as well as eggs and cocoons. Then I checked my bag of rice, which I had been using as well... and noticed they were in there too. Now I store all cupboard food in sealed containers. I fucking hate moths.
Another time I started eating one of those small boxes of raisins and it literally tasted like shit. I spat it out and threw it away. I didn't really feel like inspecting it to try to figure out what it was.