and TV shows
are often told to pretend saying while being filmed.
Mouthing this particular polysyllable (accompanied with any number of gestures) does a fine job of imitating normal speech sans sound due to the variety of phonemes it possesses. For each unique sound necessary in forming a syllable of this word, a particular face-mouth-tongue configuration is required to vocalize it - even if no sound is made. By providing a multitude of extras one simple word to mimic soundless conversation, it eliminates the need for these ersatz "actors" to come up with pantomimed "lines" on the fly and yet give them the vehicle of facial gesture and pseudo-conversation to improvise with.