There's another well known illusion, which is that sound &amp;lt;br/&amp;gt;-- it's not an illusion, it's an effect -- which is that sound can affect &amp;lt;br/&amp;gt;other senses like taste, this is researched by Professor Charles Spence&amp;lt;br/&amp;gt; at Oxford University, who found that if you put headphones on people and boost the frequency 5 kHz, they actually relate that the crisps they're eating are 15 % crunchier in their mouth, because the sound of crunch has gone up,&amp;lt;br/&amp;gt; the feeling of crunch goes up. 