The weightlessness experienced by humans in space poses a number of challenges in the performance of day-to-day tasks. Early experts feared that weightless conditions would make food difficult to swallow, allowing it to collect dangerously in the throat. Scientists began developing bite-sized cubes, freeze-dried powders, and semiliquid space foods for astronaut use, but the space travelers found the foods unappetizing(食欲をそそらない), difficult to rehydrate(水を加えて元に戻す), and messy.