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Hard baked

Why do crisp ginger biscuits go soft if left exposed to the air for a couple of days when other baked products, such as cakes and bread, go hard?

Edward Sexton, Leeds, UK

Still waters

When a container of liquid is rotated on its base in an upright position, the liquid inside doesn’t turn with it and remains static. Why is this?

Stefan Badham, Portsmouth, Hampshire, UK

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