[He's not about to spit out a perfectly good piece of candy just to click his tongue, but sucking on candy makes a sound much like 'tsk tsk.']

It's not good not to be able to show it. The killer has probably a different one, after all. One that's five paragraphs. Possibly a few more.

But, Ryuk-san is probably not the killer. Probably Ryuk-san is in the most danger...