But it is true that they so seldom smile that when they do we do not recognize their face, so distorted it is from the fixed mask we take for granted.

他们难得一笑，但当他们真的笑起来时，那张脸同我们司空见惯、习以为常的那张面具般表情僵硬的脸天差地别，扭曲得让你无从辨认。

youdao

Mask is not fixed.

面具并非固定。

youdao

The technical proposal of the utility model is as follows: the sputum suction tube (1) is fixed with an isolation mask (2) and is fixedly connected and communicated with a sputum suction mouth (3).

该实用新型的技术方案为：吸痰管（1） 上固定有隔离面罩（2），吸痰管（1）与吸痰嘴（3）固定连接相通。

youdao

The transition from one generation of consoles to the next is always painful, though this time around the launch of new portable game devices by Sony and Nintendo has helped to prop up software sales and mask the decline in sales of games for fixed consoles.

ECONOMIST: The video-games industry