Illusions may occur with any of the senses. Smell, for example. Studies have shown that olfactory (smell) illusions have occurred when subjects were given positive or negative verbal labels prior to the olfactory stimulation. Probably the most well-known and understood, however, are visual illusions, often referred to as optical illusions. They may be the most well-known because vision tends to dominate the other senses. I have a good friend who is a ventriloquist. Intellectually I understand that the voice I hear is coming from her mouth. It’s very easy to get caught up in what the “dummy” (?) is saying and perceive that the sound is coming from its mouth. After all, my brain sees the dummy’s mouth moving! Have you seen the T-Rex optical illusion?