Are your students really listening?

An interesting thought was brought up in a recent discussion:  How do you know if your students are really listening to what you are trying to teach?  I gave the first answer that came to my mind: test them.

It's something I assumed was natural.  After all, that's how all the teachers I ever met while growing up did it.  In one class, the teacher even went as far as to have random quizzes if she felt the students were drifting off.  Ah the memories...

But others in the discussion brought up interesting possibilities.  Some of these suggestions included incentives, assigned roles in a role-playing scenario, make it a contest, word bingo.  Throw in tricks was my favorite.  You (usually) announce to the class that, now that you have explained everything, you will then work through a problem on the board, but that you will purposefully do something wrong, and it is the students' job to figure out the error.  Brilliant.

My father, who is also a teacher, likes to use the following phrase whenever the students catch a small error, such as spelling:
"But I never make mistrakes!"

Now I'm wondering how I can incorporate these ideas in my next lesson...