"When he comes to his realization (Liberty IN, H. O. U. N. D.) his head jerks back with each word and there's a -zzot- noise like electricity. Imagine when you come to a huge revelation -- something you've been worrying over just suddenly clicks in your head. It's a bit like being shocked. And imagine feeling that every moment of every day because you can't stop realizing. And now imagine it x100-- that's how Sherlock feels here. Like he's being electrocuted by his own mind. It can't feel good."