Your tongue curls back, okay, and pulls back, but you also tense it up as if you clench your fist, " r" .

你的舌头会卷起来，然后缩回来，但你也会绷紧它，就像你握紧拳头一样，“r”。

Then you clench your fists like this.

然后像这样握紧你的拳头。

You clenched your fist and then you unclenched.

你捏紧了拳头又松开了。