The bird that stopped singing

Hiding a canary. Claribel grew happy and fat. Hiding her from visiting VIPs was easy, because a space station has countless hiding places. But when she was upset she got noisy, and the crew had to explain 'the curious peeps and whistles that came from ventilating shafts and storage bulkheads (walls)'. 'But then who would dream of looking for a canary in a space station?'

A strange morning. (There is no real day or night in permanent sunlight, but the words are handy.) The narrator woke with a nagging (won't go away) headache and vague memories of restless dreams. It took him ages to undo his bunk straps. Breakfast was unusually quiet, with one seat empty.

Notice: a headache, bad sleep, slowness, quietness. Each one is a symptom, a clue, and it is easy to miss them.

The bird. Sven came in and slowly opened his hand: 'a tiny bundle of yellow feathers, with two clenched (tightly closed) claws sticking pathetically up into the air'.

Jock Duncan, the cook-doctor-dietitian (expert on food and diet), listened to her chest and said honestly: 'I can't hear anything, but that doesn't prove she's dead. I've never listened to a canary's heart.'

Oxygen. Someone suggested oxygen. Claribel was tucked snugly into a face mask, big enough to be a whole oxygen tent for her. To everyone's delight she revived at once, hopped onto Sven's finger and sang, then promptly keeled over (fell down) again.

The penny drops. Something had been nagging at the narrator's memory, but his mind was sluggish (slow), another symptom. Then 'understanding exploded in my brain': 'Jim! There's something wrong with the air! 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.' His assistant: 'Er, the second alarm circuit isn't connected up yet.' Jim left without a word.

What went wrong. A rare eclipse by Earth's shadow that night had frozen part of the air purifier, and the single working alarm had failed. 'Half a million dollars' worth of chemical and electronic engineering had let us down completely. Without Claribel, we should soon have been slightly dead.'