In Now You See Me 2, the magical heist thriller in cinemas now, skilled mentalists are seen hypnotising people within a matter of seconds.

Irish magician and mentalist Keith Barry, who has hypnotised hundreds of people on stage, swears this sort of rapid hypnosis is "a real phenomenon".

Barry worked as a consultant on the film, which required him to teach actor Woody Harrelson how to do this.

But the 39-year-old performer - who hypnotised his wife to get her through childbirth without anaesthesia - tells The Straits Times that the skill can be used for nefarious purposes as well.

For instance, there have been cases where criminals have put people under and stolen their money, while the notorious "pick-up artist" community uses something called neuro-linguistic programming to seduce women.

At a press event in New York, Barry - who also worked on the first Now You See Me film in 2013 - says Harrelson and the rest of the cast were put through "what we called 'magic camp' to learn their respective skills".

"I taught Woody how to do mentalism and hypnotism, and we went out and just started doing it in restaurants and bars, with him just trying stuff."

While shooting the first movie, Harrelson, 54, may have even hypnotised co-star Mark Ruffalo, 48, getting the latter to temporarily forget the number four and see only the colour green.

Both actors now dispute what happened, though.

Barry says: "It was me, him and Mark Ruffalo at dinner, and Woody just went for it with Mark, and Mark went out. Now, Mark is a great actor. But I know when people are acting (with hypnosis) - I'm looking for things such as pupil dilation - and I swear Mark was hypnotised. But he now says he was acting. So nobody knows the real truth."

Quizzed about this separately, Ruffalo smiles. "Whatever Woody thinks happened, I'll back him up. Him and Keith Barry seem to think they actually hypnotised me and my recollection of it was very different."

Barry, 39, believes most people can be put under, though some are more susceptible. "Normally in my stage shows, I never find it a problem - hundreds of people are hypnotis- able, it's not a small minority."

And while the famous English hypnotist Paul McKenna once said reporters do not make for good subjects, Barry says journalists are not immune either.

"A few weeks ago, I was doing a hypnosis game show in the UK and was in a room with about 15 journalists. The producer had worked with Paul McKenna before and said, 'You're not going to be able to hypnotise any of them.' And I did.

"With one of the leading sceptical journalists, I stuck her tongue to the roof of her mouth and stuck her hand to the table. But it took a while - a good 10 minutes to put her into an altered state of mind.

"If you truly resist hypnosis, it makes it way more difficult, obviously. You want a willing participant. That makes it a lot easier."

This is because going under involves "shutting down the conscious mind and igniting the subconscious mind, which is where your imaginations lie", he says.

A few well-chosen words can be the key to accessing the subconscious, especially with a technique known as neuro-linguistic programming (NLP), which is based on the work of the late psychiatrist and medical hypnotist Milton Erickson.

"It's really conversational hypnosis and can be used to do all kinds of things in daily life. For me, I use it when I'm buying a house and stuff like that. I use a technique called 'yes setting' to get what I want out of the guy selling it to me," says Barry, explaining that this involves creating conversational patterns that prime the subject to say yes and tell the truth even if he does not want to.

Barry has also witnessed a man using similar tricks to try and pick up a friend of his - an approach popularised by The Game, the 2005 best- seller about a group of men, known as "pick-up artists", whose goal is to dupe women into sleeping with them.

"Pick-up artists use hypnosis. They're horrible people, it really is bad (what they do). I came across one recently in Australia, he tried it with my publicist. But we shut him down and got rid of him."

Hypnosis can also be used in another type of seduction: the one practised by politicians.

"Politicians hire hypnotists to teach them conversational hypnosis - I've been hired at home (in Ireland) for this. It's like NLP."

Asked to comment on the idea that the American presidential candidate Donald Trump may be using such tricks during his speeches, as some have alleged, Barry says: "I haven't watched enough of him, but, really, a lot of hypnosis is based on being a confidence artist. And he certainly is that."