The scientists in Bonn have solved this mystery: differences in ripeness are often invisible, but can be detected acoustically in the form of ethylene.

• 波恩的科学家已经解开了这个谜底：肉眼往往区分不出水果的成熟度，但通过水果释放出的乙烯，从声学角度探测，就能做到这一点。