Hello _Nature _readers, would you like to get this Briefing in your inbox free every day? Sign up here COVID REINFECTIONS APPEAR RARE, BUT RISKY Most people who catch and recover from

COVID-19 appear to be immune for at least five months afterwards. Interim results from a study of more than 20,000 health-care workers in the United Kingdom have found that repeat infections

are unusual — they occurred in fewer than 1% of about 6,600 participants who had already had COVID-19. The handful of people who do become reinfected can carry high levels of the virus in

their nose and throat. Such viral loads have been associated with a high risk of transmitting the virus to others. Nature | 4 min read MORE THAN 100,000 Deaths in the United Kingdom from

reality itself. Incoming US president Joe Biden faces a laundry list of challenges, any of which might seem insurmountable. _Scientific American_ offers its top four recommendations on

where to focus first, and how to achieve these goals. Scientific American | 4 6-8 min reads THIEVING MONKEYS CAN SPOT TOP-DOLLAR ITEMS Macaques at the ancient Uluwatu temple in Bali judge

which items are best to steal to earn the highest reward. Studying the monkeys’ interactions over 273 days, researchers found that macaques demanded more or higher quality food to return

items such as wallets, prescription glasses and mobile phones than they did for lower value items, such as hairpins and camera bags. The longest ransom period lasted 25 minutes, including 17

minutes of negotiation between the tourist, temple staff and thief. Guardian | 2 min read Reference: _Philosophical Transactions of the Royal Society B _paper FEATURES & OPINION TAKE A

SHORT WALK ON A CUBE-SHAPED EARTH Ever wondered how to work out the shortest path from A to B if you lived on a cube? A tetrahedron? Thankfully, we have mathematicians to explore these

parallel worlds. For solids made up of the same regular polygonal faces, the shortest straight path back to any point always passes through a corner where edges meet. Except for the

dodecahedron, which can have infinitely many straight paths that start and end on the same vertex without passing through any others. Includes some do-at-home exercises to expand your mind.

Quanta | 7 min read INSECTS FACE ‘DEATH BY A THOUSAND CUTS’ In the introduction to a special issue of _PNAS _that throws light on insect decline, ecologists do not mince words: “Nature is

under siege,” they write. “Most biologists agree that the world has entered its sixth mass extinction event.” In a bid to provide a scientifically grounded assessment of insect population

trends, the journal offers 11 papers that delve into every aspect of the issue. One of the challenges is going beyond “the overwhelming sense that something sinister is afoot” and gathering

clear, comprehensive data on insect abundances over time. There are only a handful of long-term monitoring studies of insect populations. So entomologists have turned to plumbing other

historical data for signals of change. PNAS special issue introduction | 30 min read & PNAS feature | 15 min read QUOTE OF THE DAY “The people who made it were fully modern, they were

just like us.” A striking painting of a Sulawesi warty pig (_Sus celebensis_) appears to be the oldest known representational work of art in the world, says archaeologist Maxime Aubert. It’s

at least 45,500 years old, based on Uranium-series isotope dating. (BBC | 4 min read)Reference: _ScienceAdvances _paper