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David Robson describes "earned dogmatism" as the tendency of a person to overestimate their expertise based on past training ( 23 February, p 30 ). I used to advise PhD candidates as a statistician, and was particularly aware of examiners from many disciplines who claimed sweeping knowledge of statistical methods, apparently based on an introductory …

I generally recommend you breathe in every once in a while Sabine Hossenfelder drily concurs with a finding that breathing in before doing something may make you better at it ( 16 March, p 8 )

Gina Rippon makes the points that men and women are more similar than they are different and that every person's brain is unique ( 2 March, p 28 ). She concedes that the sexes differ statistically in preferences, behaviour and abilities. How can these slight but observable differences be explained? Rippon entertains only two possibilities …

When considering sex differences , we must take into account the brain being bathed in hormones, including testosterone and oestradiol, which occur in very different amounts in most men and women. Cases of surgical and chemical castration, and of testosterone supplementation, show that testosterone levels affect behaviour, emotion, personality and cognition. In addition, the brain …

You report a 3D-printed dichroic goblet that looks brown when reflecting light and purple when light shines through it ( 9 March, p 12 ). Such effects have long been treasured. Some Victorians were obsessed by jewellery with dichroic "saphiret", made by mixing molten gold and glass. Its production ended when gold got too costly, …

The makers of the plastic goblet are a bit behind the curve. The colour of the 4th-century Roman glass "Lycurgus cup" in the British Museum shifts from red to green . The editor writes: • The researchers do mention the Lycurgus cup in their paper ( doi.org/c27r ). They suggest that since only it and …

You report the idea of CRISPR gene editing to limit the number of unwanted male calves born to dairy cows ( 9 February, p 13 ). Surely it isn't beyond us to develop a breed of cattle that lactates without giving birth? I do accept that there may be ethical or moral issues with this …

You report possible links between mouth bacteria and Alzheimer's, and note doctor Barry Marshall won a Nobel prize for linking Helicobacter pylori and stomach ulcers ( 2 February, p 6 ). Robin Warren initiated that idea, began the research and shared the prize.

• A spacecraft that slingshots around Jupiter gains energy by slowing the planet in its orbit ( 16 March, p 10 ). • The SPF rating of standard sunscreen is primarily a measure of protection against UVB rays ( 16 March, p 28 ). • The "Düsseldorf patient" seems to be cleared of reproducing HIV …

Willem Windig is surely right when he says that "illusion" is a word used far too freely (Letters, 9 March ). The one view we cannot take of consciousness and mind is that they are an illusion. If we do then, logically, that view must itself be an illusion, since it is part of our …