Katie Mitchell’s new production of Cleansed for the National Theatre has taken the Sarah Kane play’s escalating sequence of horror imagery to gory levels of realism. With the press abuzz with reports of five-or-so spectators fainting, playwright and GMT performer Andi Denny looks at the question many of us have been hard-pushed to avoid in the aftermath: how far is too far? Whenever Sarah Kane’s Cleansed comes up in conversation, it all comes back: memories of pulling my 20-y