Sherlock is finally back on our screens at last, but with the episodes so few and far between it's easy to forget some of the finer details from series gone by.
You've been watching Benedict Cumberbatch's show for years now, of course, but have you been observing. Time we found out.
Here we have a rather elementary quiz for you, we trust the answers will be obvious to sleuths such as yourselves...
How'd you fare? Tell us in the comments.