Some of them get badly gummed up, especially with children and/ or food around, so the advice from uniserver is useful. In the normal run of events, a quick rub on a clean sheet of paper does restore functionality, most of the time on most of these mice, but you have to keep at it regularly, and there are some that just get so bad that more serious action is called for. I have used alcohol on a swab in the past, and combined that with rubbing on paper, but I think I will give the more thorough uniserver method a go next time I encounter a really bad case.

It has to be said, mind you, that the overall design is so poor that the Gorgonops method might prove the more satisfying approach.