The advert also plays a cracking sound to replicate someone biting into chocolate-covered ice-cream.
One commuter said: “It sounded more like something tumbling out of a vending machine to me”.
A spokesperson for Magnum Ice Cream Company said: “The Magnum activation at King’s Cross St Pancras recreates the multi-sensory pleasure of enjoying a Magnum through sight, sound and scent, and is designed to bring a moment of enjoyment for commuters.
“Since the campaign began on 9 March, we have received mostly positive feedback from commuters onsite and will continue to optimise the campaign which is scheduled to run until 22 March based on consumer feedback.
“Our intention remains for our campaigns to be engaging and enjoyable.”