Jan is a scientist who has been asked to give a talk about their work to their lab group. 

They make slides that briefly and clearly summarise the purpose, aim, method and progress of their current project. The talk will be in their group's usual meeting room, which is quiet and allows everyone to hear what is being said. Jan's research group all speak English fluently and this is the usual language of their discussions. Jan knows that some people in the group are more familiar with their topic than others, so explains the key terms in their introduction. 

During the presentation, Jan is nervous and speaks very quietly and quickly. At the end of the presentation, several people ask Jan to repeat parts of the presentation so they can better discuss the project. 

What aspect of the linear communication model was the weakest in Jan's presentation?