Psychologists in the US have come up with what they believe to be the world's most frustrating tongue twister.

"Pad kid poured curd pulled cold" was the phrase that a team of researchers from Massachusetts Institute of Technology (MIT) in Boston found to be the most difficult to say, when repeated 10 times at speed.

Dr Shattuck-Hufnagel, the lead researcher, told the Today programme's Mishal Husain that she decided to study tongue twisters to help shed light on the "long chain of events between having an idea and actually moving your mouth to create the sound".

She added that this particular tongue twister is made more difficult by the fact that it is nonsensical.

"In a jumbled up list of words you often get people trying to say two different sounds at the beginning of the words at the same time… which very seldom happens when you are trying to say a sentence [that makes sense]," she explained.

Dr Shattuck-Hufnagel also noted the phrase "leap note nap lute" as another tongue twister that is particularly challenging to read.

First broadcast on BBC Radio 4's Today programme on Thursday 5 December 2013.