Saw your murder plans, Aconite, is it ''that hard'' to lay your hands on the flower?
John: This site is full of bloody murderers!
Sherlock: Oh, it’s rather easy. You can order it almost anywhere. The beauty of modern infrastructure.
John: Why are you helping-
Sherlock: Although I would not recommend it for murder. Given how common it is, and how messy the results are, I’d stick to a nerve toxin or something like that. Aconitum is also dangerous to handle, and any reasonable police force will investigate your internet records if you are a suspect.
Sherlock: Try nicotine. If the victim is a regular smoker, you can dissolve cigars or cigarettes in a drink. It will most likely cause a nicotine overdose, and the detectives will assume it was a case of smoking too much.
John: Have you killed people?
Sherlock: Nonsense. I just practice on the Anderson in my mind palace.