In a communication event between a first user and one or more second users via a communication network, a plurality of video streams is received via the network. Each of the streams carries a moving image of at least one respective user. The moving image of a first of the video streams is displayed at a user device of the first user for a first time interval. In the moving image of a second of the video streams that is not displayed at the user device in the first time interval, a human feature of the respective user is identified. A movement of the identified human feature during the first time interval that matches one of a plurality of expected movements is detected. In response to the detected movement, at least the moving image of the second video stream is displayed at the user device for a second time interval.