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Caroline Williams says that we are more likely to make bad choices when we are more stressed ( 27 July, p 34 ). She positions this in the context of choices we make about our health, between behaviours geared towards long-term goals, such as eating vegetables and exercising, and the short-term pleasures of chocolate, beer …

Chanda Prescod-Weinstein's lovely article on the origins and scarcity of terrestrial helium reminds me of a tour I had, about five years ago, around the chemistry lab of a leading UK university ( 13 July, p 22 ). It had very impressive, high-performance nuclear magnetic resonance machines. We asked our guide whether the liquid helium …

You report that certain whales whisper to their calves to avoid alerting predators ( 27 July, p 17 ), and that mother orangutans instruct their offspring to move on with a loud scratch ( 20 July, p 19 ). I wonder how many other animals use similar anti-predator tactics. I know the deer around my …

David Robson presents several ideas for how language might have begun ( 4 May, p 34 ). There are two more facts to consider. Twin babies often create languages. When left alone together for long periods, they spontaneously babble. This acquires form and meaning and becomes a private language – usually abandoned as they learn …

Daniel Cossins says the search for answers to the mysteries of time "takes us into the strange borderlands between neuroscience and physics" ( 6 July, p 32 ). He should include philosophy in that map. The philosopher Peter Geach argued in Mental Acts for the necessity of philosophy in such cases, saying that no experiment …

When a ball bounces, it converts kinetic energy to heat energy by deformation, so each bounce is lower than the one before. The laws of physics are generally reversible in time, but, as Cossins discusses , those involving heat, or thermodynamics, are not. Heat is an "emergent" thing: a phenomenon that appears only when we …

You report Andrew Campbell and his colleagues developing a system for employers to snoop on staff, including when they were at their desk and details about their sleep, heart rate and stress levels ( 6 July, p 9 ). Their algorithm – with an accuracy characterised as "still quite low" – classifies employees as "higher" …

I read with great interest that Europe once had its own version of a giant ostrich ( 6 July, p 17 ). I treasure a book given to me by Alice Margaret Leaker, the granddaughter of Alice McKenzie. She recalled being the last person on our planet to see a live moa, under a flax …

• Mixed messages: one air food mile is the equivalent of over 75 food shipping miles ( August, p 24 ).

You urge that we return to the moon "for all the right reasons" and say lunar bases will become staging posts for exploring Mars and the rest of the solar system (Leader, 13 July ). The "right reasons" probably won't be a priority unless we first tackle the problem of our ancient hunter-gatherer brains. Humanity …