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Max Starkey says he is bilingual and thinks in concepts and images, rather than either language (Letters, 7 December 2019 ). My experience is different. When I came round in hospital after a stroke, I was relieved to be able to understand what had happened and what was said to me, and also to be …

You write that, as yet, plastic removed by Mr Trash Wheel from rivers flowing into Baltimore harbour can't be separated into reusables, so it is incinerated to generate electricity ( 14 December 2019, p 28 ). Recycling is fine, but it only postpones the day when the plastic starts to break down into smaller and …

You mention the fundamental technology of packet switching being developed in the early 1960s by independent groups of researchers in the UK and the US ( 26 October 2019, p 34 ). Paul Baran's team at the US RAND Corporation came up with the idea of independently routed "message blocks", while researching ideas for networks …

Donna Lu reports on a search for unprecedented forms of life ( 16 November 2019, p 42 ). But how can we tell what is alive? In Canada, there are frogs that freeze in winter and thaw out in spring. During dormancy, are they alive or dead? If living, they don't conform to any current …

I was interested in your article about those who need very little sleep ( 26 October 2019, p 18 ). I am one such person and, at age 77, I would like to meet others. Some of my relatives and ancestors have or had the same ability. In relationships, like attracts like. "Never sleepers" tend …

Gege Li reports work to modify bacteria so they consume carbon dioxide instead of sugars ( 7 December 2019, p 19 ). This clearly requires energy: that would have to come from the sun or from chemical energy, and supplying the latter generally involves producing CO 2 . I would hope to see a more …

• Brass is an alloy of copper and zinc, and bronze of copper and tin ( 14 December 2019, p 10 ). • A white dwarf star is made of atoms, and doesn't collapse further because that would require their electrons to occupy the same energy levels, contrary to the rules of quantum physics ( …

Annalee Newitz gives plenty of reasons not to have an internet-connected smart doorbell with a camera ( 14 December 2019, p 24 ). I suggest another. Hackers will scrutinise any mass-market, low-cost, internet-connected device and will almost certainly find a security flaw. If they do, such devices offer them a gateway past the security in …

Roger Morgan suggests that humans may get more stressed in a self-driving car than when driving themselves, as it seems rats that have been taught to drive a tiny car do (Letters, 30 November 2019 ). Living in Switzerland, with its many sinuous mountain roads, I can think of one example where this is clearly …

Describing the damage done to wildlife by cats roaming outside, Lawton suggests that keeping them indoors wouldn't suit them. As a cat lover and owner, it seems to me that a cat raised indoors from kittenhood is perfectly well-adjusted and healthy. We should convince new cat owners to consider only house cats. The comfort, affection …