The cabin was dark, and Tom Garret was asleep. He was warmed and comforted by ever-present hum of the the ship. Even while the ship was on its long glide, her reactor let out a sinusoidal pulse, embracing the crew in a warm and steady heartbeat.
Spacefarers knew this sound and loved this sound. It brought the feeling of kinship with their vessel. It was the sound of security in a massive and empty void, of their bubble of safety in the millions of miles of emptiness between them and their destination.
So when the reactor developed a murmur, Tom stirred. It was subtle. It may be hard to notice one extra beat among the thousands. It was too easy for a conscious mind to ignore such a shift and simply dismiss the unevenness as a mistake in perception. But a sleeping mind can sour, and Tom's did.