What were Sherlock's best deductions in the books?

I know this 问题 is very hard but I'm wanting to do an oral at school on Sherlock and I want some of his deductions that are short and easy to understand without having read the story.

I have one which goes something like "Human behaviour leads us to write above eye level" when Sherlock was able to deduce a height just 由 having a person write on the 墙 in The Study of Scarlet (He was also able to tell it from how the person walked but I liked the 写作 on the 墙 one better).

If 你 guys can help that would be great. Also if 你 have any ideas of what would be good to have in an oral on Sherlock, then please say, I'm open to ideas here :).