When we wish to persuade a person to perform an action, think a thought or behave in a certain manner, we want to do so in a way that the person won't ever suspect us as influencing such a thing.

We do this by wording our suggestions in such a discreet manner that the person won't pick up anything amiss. This can of course be easier said than done, however with practice this will become a seemingly natural, intuitive process. One of the main things you want to pay particular attention to is the person's body language. If the person looks slightly uncomfortable, or looks at you in an awkward manner, then this could be an indication that your suggestions are becoming a little obvious, and the person may even become consciously aware of them. This would be a good indication for you to lighten your suggestion a little.  The sort's of body language you want to pay attention to include the person's eye cues. We know from NLP that if a person moves their eyes in a certain direction then they're accessing a representational system, namely either an auditory, kinesthetic or visual rerpsentational system (each of which is either remembered, constructed or in the case of auditory, also internal).  What we can do is mention a certain phrase or sentence and look at the person's eye cues to try and determine whether or not the person is moving their eyes in a direction that we expect. If they're not, then this could be an indication that appropriate rapport hasn't been established.   For example, let's say we're talking about a beautiful sunset beach in some distant place. We would expect the person to move their eyes in an upwards direction if they were comprehending what we were saying, since this would indicate that the person would be thinking of a visual thought. Now let's say instead the person moved their eyes in a downwards direction. This could indicate the person was instead using their internal voice, perhaps indicating that they weren't following our lead at all.  We have to always test to make sure that the person is comprehending our suggestions, and we do this by predicting and expecting eye cue movements. If the eye cue movements aren't what we predicted, then we should establish even deeper rapport to ensure that the person does feel comfortable with our suggestions.  So it is possible to use covert hypnosis outside of a person's conscious awareness, however we need to make sure that the person is, at the very least, consciously comprehending our sentences.  

Steven Peliari is a Master Hypnotist and Chairman of the International Hypnosis Association. He has recently released his famed best selling course The Art Of Covert Hypnosis, which teaches people how to use covert hypnosis discreetly.