article_snippet: Scroll down for video .
article_snippet: These defences are expressed in These defences .
article_snippet: But this rose to a piercing screech when this was under threat.
article_snippet: the plant is subjected to stress, the louder the signal,' said Dr Frank Kühnemann.
article_snippet: But different sounds are heard when the gas different sounds emit, ethylene, is bombarded with lasers.
article_snippet: The research could then be separated from the fresher ones.