[Sherlock doesn't want Mycroft looking at his arm, he doesn't know how far ahead his brother is and he'd rather not deal with the potential lecture that seeing relatively recent track marks might spark.]
Why?
[He huffs.]
Let me make a deduction, you think you saw something. You didn't, hallucinations are common here.
cw: mention of drug use
Why?
[He huffs.]
Let me make a deduction, you think you saw something. You didn't, hallucinations are common here.