Revealing mistake: Cottontail gives Tom a wet Willie. However Tom reacts before Cottontail touches him.
Revealing mistake: When Tom is fired from Harrods, he is escorted out of the building. Look closely in the glass to the sides of the doors, mainly the screen right, to see a group of people just stood watching the film crew. There is a slight hint of a barrier visible around waist height but to spot the barrier you have to look extremely closely. (00:17:00)
Answer: It's not clear if he actually can hear them or not. It's implied in the film that it's possibly stress or a mental break that is causing him to hallucinate their voices, or is suddenly thinking on a brain wave length that can understand them. If it's the former, it's coincidence that he hears similar to what Peter is actually saying. Either case explains why he suddenly can hear them when nobody else can around them despite them talking in front of people.
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