What is invisible, but can still make some people cough and splutter? This week's Big Picture offers pupils another chance to be picture detectives and, with a little help from their friends (you included), use their eyes and imagination to work out what the strange creature might be. (Don't forget to cover up the words when you show the picture.) Questions
1 Roughly how big is this creature? As big as a pinpoint? A penny? A sparrow? A cat? A sheep? An elephant?
2 What does it eat for breakfast?
3 What does it remind you of? What does it look like?
4 How could it harm some people?
5 What do you think it is?
1 A pinpoint (the photo makes it look much bigger than it really is, but 300 laid end to end would barely be an inch long).
2 You (your dead skin, to be exact).
3 A spider or a scorpion (it is a member of the arachnid family, so it is not an insect, as it has eight legs, not six).
4 By getting up your nose - literally. (If you are sensitive to them, their corpses and faeces can make you cough and sneeze. For people with asthma it can cause an asthma attack, by making the tubes in their chest sticky with mucus, a bit like hayfever does).
5 A dust mite.
It is important to avoid frightening children, so explain that doctors can help the few people who suffer attacks with treatments like antihistamine.
Ted Wragg is professor of education at Exeter University.