I have often been critical of the "Grammatically Speaking" columns put out occasionally by TESOL, but the most recent is, I think clear, accurate, and interesting. It looks at the the question of why we say zero degrees instead of zero degree. Something I've brought up here before.
Schmitt points out that the terms plural and singular may be misleading, and suggests singular and nonsingular. This I think, is a useful approach.
As for his brain teaser, these usually strike me as fairly obvious, but this time, I have no idea what the issue is. Any insight?