Five cards a day.
A little sharper.

To the eyes of a deer, what does a tiger’s orange coat look most like?

Green, like the leaves. Deer have two kinds of colour cone, not three, so orange and green give them the same signal. Fennell and colleagues modelled this and found the tiger nearly matches foliage for its prey while standing out to people. Mammals cannot make green fur; orange is the nearest thing that works.

The trap: Assuming the prey sees the same bright orange that people see.

Source · Fennell et al., J. R. Soc. Interface, 2019

A rope hugs the equator. Add 1 m to its length and raise it evenly all round. Can a cat crawl under?

Yes, easily. A circle’s circumference is 2π times its radius, so adding 1 m to the rope lifts it by 1 ÷ 2π, about 16 cm, all the way round — whatever the size of the circle. The same extra metre around a football would lift it by the same 16 cm.

The trap: One metre spread over 40,000 km feels like nothing at all.

Source · Circumference and radius of a circle

A deep-sea octopus in Monterey Canyon guarded one clutch of eggs. For how long?

About 4.5 years. Researchers recognised the same Graneledone boreopacifica female by her scars on 18 dives between May 2007 and September 2011, about 1,400 m down; she was never seen eating. Cold water slows development, so her roughly 160 eggs took 53 months to hatch, the longest brooding known for any animal.

The trap: Shallow-water octopuses brood for weeks or months, so months sounds right.

Source · MBARI release via EurekAlert, 2014

A builder arrives in agony with a 15 cm nail through his boot. Sedated, the boot comes off. What did doctors find?

The nail between his toes. It had gone through the boot without touching skin, yet he needed strong painkilling sedation before anyone could pull it out. His brain produced real agony from what it saw and expected. Pain is the brain’s judgement of danger, not a direct reading of damage.

The trap: A wound right through the foot, since agony like that must mean damage.

Source · Fisher, Hassan & O’Connor, BMJ, 1995

When SOS became the international distress signal in 1906, what did its three letters stand for?

Nothing at all. The 1906 Berlin radiotelegraph convention chose it for its Morse: three dots, three dashes, three dots, sent as one unbroken pattern that is hard to mistake even through static. Save Our Souls was fitted to the letters later. Engineers picked a sound; storytellers supplied the words.

The trap: Save Our Souls, because a signal that urgent must say something.

Source · International Radiotelegraph Convention, Berlin, 1906