It's a way of taxing consumers without telling them they're being taxed.

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The Dutch study exposed volunteers in laboratories to radiation from 3G and "traditional" masts - without telling them which version they were being exposed to.

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You can only record at a lower resolution, but it's still fun to capture a friend in slow-mo without telling them and then embarrass them when you play it back.

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Or to put it another way, telling banks they have to raise material amounts of capital - without telling them how much capital and setting a deadline from them to find it - may have the perverse and damaging consequence of contracting the amount of credit supplied to the economy, and knocking economic recovery yet again.

BBC: How big is the 'material' hole in banks?

Thus, it provides doctors not so much a recipe for treatment, but a sense of knowledge, empowering them to make informed therapeutic decisions without explicitly telling them what to do.

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Half said they told their patients that the therapy had helped other patients without specifically telling them that they were prescribing a placebo.

BBC: 'Most family doctors' have given a patient a placebo drug

Some states have co-operated with each other, even without the federal government telling them to do so.

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