Really Close Surveillance

In a darkened van, one surveillance operative brings coffee and asks his colleague on the line whether the bugged targets have said anything yet. The answer is a vague warning about watching your words. The scene then cuts to a second van, where another pair of operatives is listening in and reaching the same unsettling report, until one of them realises his own words are coming back to him. A final exterior shot reveals the two vans parked nose to tail, each team spying on the other.