I'm baffled by your usage of the word "grain", especially when you say you thought it was a "normal grain". It's difficult to respond since there's no such thing. I can only presume you stating it resembles something like a grain of salt or something (small in size). HPV warts can come in many different forms, raised or flat, pinkish or flesh colored, single or multiple. Since you haven't been specific as to the exact location of this lesion it's also hard to distinguish what else this may be. Perhaps you could provide more specific info.