During the course of a lecture, students' reactions and posture can be used to draw conclusions about their understanding and concentration. Reactions should be addressed openly. A question about understanding or lost connections helps all students to reflect briefly and motivates them to comment if necessary.
The offer of feedback should be as low-threshold as possible. This can be achieved, for example, by using a humorous formulation: "Your question will relieve twenty others in the room".
If necessary, the teacher can offer a follow-up by providing additional information or another form of preparation.