But so far the virus has not shown itself to be more severe than seasonal flu.

VOA: special.2009.08.05

And also, it's useful because harmful stimuli are noticed but when something has shown itself to be part of the environment you don't notice it anymore.

而且它还是非常有用的,因为危险刺激会吸引到你的注意,但当某物被视为环境的一部分时,你便不会再去注意到该物体。

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