How much can you trust your eyes - or your other senses? We need to trust them to function and be safe, but they can be easy to fool and this makes for interesting science lessons.

One optical illusion can be used to explain how we see colour. Make a union flag, but substitute cyan for the red, black for white and yellow for blue. If you stare at the flag for 30 seconds then look at a sheet of white paper, a proper red, white and blue flag appears. The explanation? The retina has two types of cells - rods that detect shades of grey and cones that react to different colours. Staring at a colour triggers the signal for that colour, but not others. Staring over-stimulates certain cones. Once you look away, the cones and rods that haven’t been stimulated react and you “see” the “correct” colours.

Your temperature senses can be fooled, too. Take three buckets, one filled with ice, one with hand-hot water and the third with water at room temperature, then get pupils to put one hand in the hot water and the other in the ice water for a few seconds, then plunge both hands into the room-temperature water. They will find that the hand that was hot is now cold and vice versa.

A lot of what we taste is what we see and smell. Try getting pupils to taste different-flavoured crisps while blindfolded with nose-clips on. It can be hard to tell smoky bacon from prawn cocktail, or even salt and vinegar.

Scientists often use measuring instruments rather than just their senses to gather information. Carrying out some simple experiments is a useful way to discuss how scientists work. In short, we shouldn’t always trust our senses.

James Williams is a lecturer in science education at Sussex University. His book `How Science Works: teaching and learning in the science classroom’ is published by Continuum (pound;19.99)

What else?

Try a Hamilton Trust lesson plan to explore how people use their senses when they are sight or hearing-impaired

Ericag’s “five little senses” poems are a big hit with teachers and have been viewed nearly 50,000 times. Try them out and tell us what you think

In the forums

Teachers share their methods for fun sensory investigations

All links and resources at www.tes.co.ukresources006.