One possibility.

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Note added at 4 mins (2008-11-14 23:57:39 GMT)
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http://archive.lancashireeveningtelegraph.co.uk/1998/5/26/80...

Assim o diria, como nestes exemplos:

mindblob: Is viral marketing dead already?
You touch a sensitive point there... marketing is supposed to be as rational as possible, but when it comes into the hands of the consumers, I am convinced ...
mindblob.typepad.com/mindblob/2007/07/is-viral-market.html


NHL | Member profile
When you talk about Sidney Crosby, you touch a sensitive point. And if you dont say what EVERY people want to hear (he’s the best) you’ll remember it for a ...
http://fans.nhl.com/OnyxHawke

Nerves And Common Sense: Chapter XXVI
... mass of exciting and painful emotions which can be aroused to a boiling point at any moment by anything or any one who may touch a sensitive point. ...
www.soilandhealth.org/03sov/0304spiritpsych/030407call.nerv...

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Note added at 27 mins (2008-11-15 00:21:03 GMT)
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The link to the first example is:

http://mindblob.typepad.com/mindblob/2007/07/is-viral-market...

Outra sugestão:

Idiom Definitions for 'Open old wounds'

If you open old wounds, you revive a quarrel or problem that caused a lot of trouble in the past.

http://www.usingenglish.com/reference/idioms/open old wounds...

14 Nov 2008 ... Clearly we’ve hit a sore point. Indeed, some chefs hold onto their private little kitchen grudges for decades. “It took me awhile to learn ...
blogs.dallasobserver.com/cityofate/2008/11/burning_question_which_ingredi.php

... reaction against Yilmaz from within both the military and the political establishment indicates that the leader of ANAP had indeed hit a sore point. ...
www.ciaonet.org/wps/jud03/

The profs seem to have hit a sore point. How could a couple of obscure business professors get the mighty Investment Company Institute into such a lather? ...
www.forbes.com/forbes/2004/0301/046.htm

Entendo que "colocar o dedo na ferida" é tratar de um tema sensível, difícil.

Portuguese term (edited): pôr o dedo na ferida de uma questão crucial do mundo moderno

None of the answers offered thus far really work in the present context. The most plausible of these, Marlene's "pour salt into the wound" suggests a deliberateness and aggression that seems inappropriate for the description of a work of art--no matter how provocative it may be.

In my view, there is also no need to translate the phrase "de uma questão crucial" here, for it contributes little to the meaning of the phrase and instead encumbers the language with unnecessary verbiage.

Boa sorte.