Drive across a long bridge and you'll thump over a strip of metal teeth or a rubber seal. That's no repair job. It's a deliberate gap, there to let the bridge grow and shrink with the weather, because trying to stop it would be far more dangerous.

The swirling rainbow on a soap bubble isn't dye, and it isn't a reflection of the sky. It's light bouncing off the front and back of a film so thin that the two reflections interfere with each other. Watch a soap film drain and the colours slide downwards until the top goes black. That black patch isn't a hole. It's the thinnest part of all.

Partway through the first volume of Tristram Shandy, the words simply stop. Both sides of a leaf are printed solid black, a funeral in ink for a character who has just died. It wasn't quite as unprecedented as legend suggests, and that turns out to be the interesting part.

In the kula exchange of the Massim islands off eastern New Guinea, as Malinowski described it in the 1920s, prized shell necklaces and armbands travelled in opposite directions around a ring of islands. Some were famous, and hardly anyone held on to one for long. In that account, prestige came from holding famous pieces and passing them on.

A dinosaur trackway contains no bone at all, just a line of prints in rock that was once mud. Yet it records something no skeleton can: what an animal was doing for a few seconds while it was alive. The catch is that footprints are surprisingly bad at telling you who made them.