In this activity about light and reflection, learners discover that what you see is often affected by what you expect to see. Learners hold on to a device consisting of two mirrors glued back to back to each other with a dowel handle on either side. While looking at one side of the mirror, learners move one hand on the other side of the mirror. They will be surprised as their brain is fooled into thinking that the image it sees in the mirror is actually their other hand. Learners can participate in assembling the mirror device or use a pre-assembled one. This resource also includes a simpler version of this activity in the "etcetera" section at the bottom of the guide.