“I don’t get it,” lamented Sven. “What’s wrong with her? She’s never done this before.”

For the last few minutes, something had been rugging at my memory. My mind seemed to be very sluggish that morning, as if I was still unable to cast off the burden of sleep. I felt that I could do with some of that oxygen—but before I could reach the mask, understanding exploded in my brain. I whirled on the duty engineer and said urgently:

“Jim! There’s something wrong with the air! That’s why Claribel’s passed out. I’ve just remembered that miners used to carry canaries down to warn them of gas.”

“Nonsense!” said Jim. The alarms would have gone off. We’ve got duplicate circuits, operating independently.”

“Er—the second alarm circuit isn’t connected up yet,” his assistant reminded him. That shook Jim; he left without a word, while we stood arguing and passing the oxygen bottle around like a pipe of peace.

He came back ten minutes later with a sheepish expression. It was one of those accidents that couldn’t possibly happen; we’d had one of our rare eclipses by Earth’s shadow that night; part of the air purifier had frozen up, and the single alarm in the circuit had failed to go off. Half a million dollars’ worth of chemical and electronic engineering had let us down completely. Without Claribel, we should soon have been slightly dead.

So now, if you visit any space station, don’t be surprised if you hear an inexplicable snatch of bird song. There’s no need to be alarmed: on the contrary, in fact. It will mean that you’re doubly safeguarded, at practically no extra expense.