Professor Richard Wiseman and Emma Greening recently wrote a paper about studies on suggestion and influence regarding that classic PK effect 'bending a key'! Magic enthusiast Richard Wiseman discuses an experiment in which two groups were shown the same short film where a bent key was placed on a table, it was suggested to the first group that the key was still bending, while the other group, watched the same footage, with no suggestions.
It comes as no surprise to us magicians that the first group claimed to see the key continue to bend.
As we performers are aware if we continue to tell our audience that the object is still bending, (especially while performing some clever little moves), the audience is more likely to not only believe this, but also to 'see' it.
   There are two types of performers who present this, the first being the performer who claims to be able to bend the item using 'mind powers' for example Uri Geller has always claimed that his mind has the ability to alter the composition of the metal in the item and so it bends; whereas the second type, magicians/mind readers who bend keys and cutlery do so, not as 'mind powers' but as more of a strange magical feat.
  Let us consider the use of the 'continuing to bend' suggestion, whether on the table or in the spectators hands.
As a magician if your audience and volunteers believe that the object did continue to bend while in their hand or on the table, you have performed some amazing magic, you were not merely demonstrating sleight-of-hand but instead creating a really magical experience for them.
  What suggestion? For this we rely on the 'presupposition'.
For example:  "Do you see it bending?" A close ended question, it is bending or it is not bending.
"As it continues to bend you might see it flicker in colour or get lighter for a brief moment or two?" a presupposition that it is still bending.
It is just a question of whether you are aware of the colour changing slightly or it getting lighter as it continues to bend.
There is also an ambiguity here, when spoken in this sentence it is unclear whether you mean lighter in colour or weight, this further adds to compound the suggestion.
  Decide upon what you wish your spectators and volunteers to experience, then construct a sentence that can only be true if what you want them to believe is actually happening.
The more presuppositions you use in one sentence the more the conscious mind is likely to accept them.
  As you read over this last bit again (presupposes you are going to read over this again) and realise that you already use presuppositions (presupposition that you will realise this) and decide (presupposes you will decide) to take a few moments to think about new ways (presupposes there were old ways) of using them, either now or while performing (presupposition that you will do this either now or later) the more you learn (presupposes you are learning) and the more fluent (presupposition that you are to some degree already fluent) you get at using presuppositions