When Jeremy reaches through the tube to the interior of the car, he pulls back his hand with two knuckles scraped raw and a cigarette lighter burn on his hand. The knuckle wounds remain but the cigarette lighter burn disappears within seconds.
With short wave radios, the person speaking must press a button to engage the microphone to broadcast, and cannot receive signal while the button is depressed. In other words, only one person can speak at a time. This is why people say "over" when they have finished speaking-- to indicate that they have finished taking their turn. It is not possible to interrupt someone while they are broadcasting, as is depicted in the movie several times.