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You report three studies that indicate covid-19's adverse impacts on the immune system 15 May, p 10 . In particular, Verena Kaestele's work highlights abnormalities of the innate immune system, with the suggestion that this may contribute to long covid. Certain long covid symptoms are frequently likened to illnesses such as chronic fatigue syndrome (CFS). …

James Wong reports that the calorific value of celery after chewing and digesting it is tiny, but not negative as some people believe 22 May, p 24 . A few years ago, I read an article that came to the same conclusion, but expanded it by stating that if the celery was eaten when very …

There is much speculation about odd plants on other planets, but arguably such life is already found close to home, often in the garden centre 8 May, p 46 . Black mondo grass ( Ophiopogon planiscapus 'Nigrescens') has black leaves; a type of pore on the leaves of silver saxifrages secretes calcium bicarbonate, possibly as …

To say "astronomers are in little doubt that a plant-filled planet exists beyond our solar system" may be going too far. A few years ago, speaking of how views on life elsewhere have changed since the 1960s and 70s, physicist Paul Davies said the prevailing view was that its emergence here was a bizarre fluke, …

You reported the benefits of cold-water swimming 13 March, p 46 . I shower daily in water as hot as I can stand and feel most of the benefits attributed to cold water. I wonder if this has been researched. In any event, hot water is much more pleasurable.

There is a paradox behind Japan's use of the Olympics to promote a hydrogen economy ( 29 May, p 18 ). Japan is short of space to build solar and wind farms. However, the country intends to build a solar power station to generate the electricity it will use to produce green hydrogen, even though …

Fuelling the Olympic flame in Japan with hydrogen has a drawback: hydrogen burns with a very pale blue flame that can be quite invisible in daylight. An obvious remedy would be adding quantities of butane, say, to bring back a cheerful yellow flame, but that would defeat the point of using hydrogen. Perhaps a small …

I read with interest and fascination the article on the platypus and the echidna , both of which I have seen in Tasmania, where my brother lives ( 8 May, p 41 ). What an extraordinary world we live in. However, I was taken aback when the article stated "it would be a shame if …

You report that rocket companies are planning to send tourists into space and wonder when the democratisation of space flight will happen ( 29 May, p 16 ). Huge amounts of energy are required to send anything into space and it seems likely that much or all of this energy is provided directly or indirectly …

Yes, human birth is difficult compared with that of other primates, as you report, due to differences in pelvic evolution ( 15 May, p 12 ). However, many difficulties in childbirth today are caused by immobilising the mother and making her fetus work against gravity. If we allowed the mother and her fetus greater freedom …