He touched his wife's arm with that finger, indicating to her that he wanted her to call the engineers again. Then he used the same method of tapping her arm to tell the engineers what to do.

他用手指碰了一下妻子的胳膊，就是在告诉她，他想让她去喊工程师，再用同一方法轻拍她的胳膊，告诉工程师去做什么。

youdao

Then he used the same method of tapping her arm to tell the engineers what to do.

然后，再用同一方法轻拍她的胳膊，告诉工程师下一步怎么做。

youdao

You can try tapping your fingers on the desk or the chair's arm-rest.

你可以试着用手指敲桌子或者座椅扶手。

youdao

So, using Skinput, someone could send text messages by tapping his or her arm in certain places -- without pulling the phone out of a pocket or purse.

CNN: Microsoft's Skinput turns hands, arms into buttons

The gestures could be either big ones like arm waving, or subtle ones like tapping your finger on your thigh or coffee table.

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