Listeners normally provide speakers with simultaneous feedback such as nods, "yeah"s and "mhm"s. These`backchannels' are important in helping speakers to talk effectively. Two factors are known to influence when a backchannel is produced; if the speaker is looking at the listener or if the speaker is presenting new information. We investigate a third factor: whether the speaker is having trouble speaking i.e. self-repair. If dialogue is an active collaborative process then listener's responses should be especially critical when trouble is encountered. Using data from a corpus of three person dialogues we show that speaker's rate of self-repair is a better predictor of listener responses than speech rate. We also show that listeners respond strongly to speaker troubles independently of whether the speaker is looking at them. We argue that it is the points at which conversation threatens to go off-course that are most significant for coordination.