For a quick filler in such a lesson (illusions) try this one:
http://brainwaves.corante.com/archives/2007/10/31/a_scary_illusion_mr_angry_and_ms_calm.phpUnfortunately the original page is down, but if you can find a reasonably large copy then print it out as large as you can (on A3 or B4 paper).
Here's how I use it.
Stand in one corner of the classroom (say, front left). Don't show the image yet (I usually fold it gently with the short edges together). Explain you have a photo of Mrs. Calm and Mr. Angry (good opportunity for vocab. and making faces). Ask the students to raise their hands on the side that Mr. Angry is on. Show the picture. The students near to you and the students far from you will put up opposite hands, but they might not immediately realise this.
Next, fold the picture and walk to the next corner (say, front right). Same routine- which side is Mr. Angry on? The students at the front should be surprised that Mr. Angry and Mrs. Calm have swapped places, but the students at the back are probably far enough away that no change is visible.
Do it again at the other two corners. It's a startling illusion.
For extra points, show the picture and hold it in front of you while you walk from a distance towards a group of students. You will get big wows when the image flips.
I use this for the Guilloteaux book for 2nd year Middle School, Lesson 6 "Learn to control your anger". The key expression is "That's impossible!".
