I know we usually use some in questions when we offer things or ask for things: Do you want some more cake? Can you lend me some sugar, please? It is also said that we can use it when we know that the answer is going to be yes. However, I have just seen this sentence, it is written in a coursebook and in fact, there are many more like this one: When did you last eat some chocolate? we are not offering things, asking for things, and the answer cannot be Yes. So why some? I must admit that I would never use any in this sentences, but I don't know why.