You've sewn your torn cuff together with a Lembert stitch, which, of course, only a surgeon uses.
6 seconds sound clip from the The Great Mouse Detective movie soundboard.
You can hear this line at 00:08:11 in the Blu-ray version of the movie.
Quote context
[...]
- Wait just a moment. How did you know I was a doctor?
- Just returned from military duty in Afghanistan, am I right?
- Why... Oh, yes. Major David Q. Dawson.
- Uh... But how could you possibly...
- You've sewn your torn cuff together with a Lembert stitch, which, of course, only a surgeon uses.
- Amazing!
- Actually, it's elementary, my dear Dawson.
- What in heaven's name? Oh! Oh... My...
[...]