Kathy,
I agree we can set the mood. It is also true that sometimes students arrive in a "funk" and regardless of the enthusiasm shown by the instructor, the students just ar'nt there or engaged. That's when I will do a change up - a different activity to get students up, moving around, involved and interacting. Someehow, keeping busy through involvement helps break the funk and class time is not wasted that day.
Barry Westling