Silence is an area of study that receives relatively little attention from second language (L2) researchers, who in the past have tended to concentrate more on the spoken aspects of discourse within classrooms. Far from being merely communicative voids in which nothing of interest happen, moments of silence during educational encounters are actually rich in form, function and meaning. This talk will report on a large-scale, multi-site investigation into the silent behaviour of L2 learners attending English classes within Japanese universities. Using a complexity perspective as its conceptual background, the investigation moves away from traditional, reductionist, single-cause explanations for learner reticence to suggest that silence actually emerges through multiple, concurrent routes. These routes are so abundant, and appear to be so well supported both educationally and culturally in the Japanese context, that silence appears to have fossilised into a semi-permanent attractor state within university language classrooms.