The holes in Emmental are carbon dioxide. Bacteria make the gas while the young cheese ripens, and it pushes the paste apart into the round eyes everyone draws on cartoon cheese. That much has been understood for about a century.

What nobody could explain was why the eyes were thinning out. In 2015 Agroscope, the Swiss federal agricultural research centre, gave the answer: hay. Microscopic particles of it, carrying even smaller pockets of air, used to drift into open milking buckets in the barn. Milking moved to closed machines that pipe straight into tanks, and the particles stopped arriving.

The bacteria didn't change. They kept making gas. But with nothing to collect around, most of it simply left the cheese. A follow-up note from Agroscope put it flatly: the particles decide only where the holes form, and how many.

I keep turning that over. The gas is the same everywhere in the wheel. What differs is whether, at one exact point, there happened to be a speck of something for it to gather on. Every eye in a slice of Emmental marks where a bit of a field was, and a hole is not made by what fills it.

The same note was irritated with reporters who had called the particles dirt, and fair enough. Five to ten milligrams of hay in a thousand kilograms of milk is enough for a typical set of holes. So the fix is to put it back on purpose: a pinch of the barn, weighed out, so the gas has somewhere to start.

When a storefront sign comes down, the wall often keeps saying the name.

Dimensional letters spend years shielding small pieces of brick or stucco. Sun fades everything around them. Rain leaves tracks. Soot settles at the edges. Then the landlord unbolts the word, and a cleaner version appears underneath: not the sign, but the weather it prevented.

I like these pale names more than most preserved signs. A painted ghost sign is an image surviving. This is an image produced by removal. The shop has to disappear before the wall can show how long it was there.

The mounting holes add punctuation. A capital letter becomes six bright islands and three black dots. Sometimes the outline is more legible than the original logo because nothing is trying to sell anything anymore.

For a little while, before the next tenant covers it, the facade becomes a photograph developed by exposure. The name is made from unequal aging: one surface allowed to weather, another kept young behind plastic and steel.

A brand pays to occupy attention. By accident, it also occupies sunlight. Years of blocking the sun become its last advertisement.

A lifeguard's zone is drawn on paper first: a pool plan with lines across it, one shape per chair. The CDC's model code for public pools says what the shape must do, not how big it may be. The guard has to see all of it and reach its furthest point within twenty seconds. The unit is not a foot. It is twenty seconds of one person getting out of a chair.

So the drawing is checked with a body. Someone waits at the far corner of the zone and the guard is timed from leaving the stand to touching them. If the second hand gets to twenty first, the chair moves, or the line does, or a chair is added. The shape was wrong, not the swimmer.

The other check is sneakier. A dark silhouette of a swimmer is rolled up like a towel, or hidden under a swimsuit, or handed to a member of the public, and goes to the bottom while the guard is looking the other way. The clock starts when it is fully under. Ten seconds to see it, twenty to reach it, and the guard has to go in — pointing does not count. The guidance is one of these every forty hours on duty.

In 2001 a lifeguard-auditing firm and a company that sells drowning-detection cameras dropped manikins more than five hundred times across ninety-odd pools. Guards saw them inside ten seconds in nine percent of the tests. The average was a minute and fourteen. The camera company had a product to sell.

What I like is what the drill admits. A lifeguard is paid to watch for something that, on any one guard's watch, almost never happens. So the pool manufactures it — a drowning on schedule, made of rubber — and the guard cannot know which kind it is until they have it in their hands. The design only works if they never can.