It's often helpful when teaching to know what mood the class is in. One quick way to do this is to take the group's "pulse." Go around the room and have each student state one word that describes how he/she is feeling at that moment. It can be ANY word. Taking the group's pulse at the beginning of the hour can be very useful in understanding why individual students, subgroups, and the class as a whole react the way they do to the lecture or activity for the day (if you get many students saying "tired" and "stressed," they may be very quiet during the class period... and it's not due to a deficiency in your teaching!). You can also take the group's pulse during or at the end of the hour to assess their reactions to the class.
Taking the class's pulse also can be used as a preliminary step in doing mood role plays.