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Michael Harrison suggests that neural networks should have a "don't know" output (Letters, 30 June ). If he visits the mathematics gallery of the Science Museum in London he will find the London Hospital Survival Predictor , which I invented in 1972. It used two "classifiers" on electroencephalograph data from patients in a coma after …

Clare Wilson is not entirely convinced by Edward Bullmore's argument in The Inflamed Mind that mental adversity causes inflammation, which then causes depression ( 30 June, p 46 ). Our bodies may be facing many potential hidden stressors, so I wonder why emphasis is placed on psychological stress as the most important driver of the …

I remember at school being told people used to use spiderwebs on injuries to help clotting Eve Coy makes an old connection with new work on artificial skin grown from spider silk that could help heal wounds ( 21 July, p 17 )

Researcher Frédéric Lechenault concludes that the stretchiness of knitting is due to the way interlocked stitches spread friction through the fabric, based on an assumption that the yarn itself doesn't stretch ( 30 June, p 19 ). Perhaps he should watch someone knit a scarf. Depending on what pattern of stitch a knitter uses, they …

Peter Wilson is enthusiastic about electric aircraft ( 30 June, p 24 ). But one problem they face is that an empty battery weighs just as much as a full one, whereas a liquid-fuelled plane gets lighter and more efficient as its tanks empty. So can we jettison empty batteries and recover them? I recall …

What Wilson fails to mention is that the heavier the plane , the more energy it takes to get from A to B because more lift is needed and there is more drag. About half the weight of a liquid-fuelled long-range flight at take-off is fuel. We need instead to develop liquid fuel that doesn't …

Your encouragement in one issue to think about both consciousness ( 30 June, p 30 ) and Schrödinger's cat ( p 34 ) raises interesting questions. When Schrödinger originally formulated his conundrum, he postulated that a single conscious entity making an observation would determine the fate of his poor entrapped moggy. Subsequently the conundrum was …

Schrödinger's cat is one of the great non-questions. Anyone who has ever owned (or rather been staff for) a cat will know that it is conscious and self-aware, so would be perfectly capable of collapsing the wave function itself. Maybe it would be worth discussing "Schrödinger's bacterium"?

Rob Bayly asks why you don't post Â鶹´«Ã½ in a paper pack and you say you are reviewing this (Letters, 23 June ). I live in the tropical far north of Queensland in Australia, and look forward to seeing my magazine each week in the mailbox at the end of our drive. During the …

• When 900,000-year-old skulls were found at Yunxian in China, Homo sapiens was generally thought to have evolved in Africa at some time between 100,000 and 200,000 years ago ( 7 July, p 28 ). • The genome-edited soybeans that are being grown commercially in the US this year were created using a genome-editing technique …