The corners of her mouth trembled as she tried to smile.

The corners of his mouth were trembling a little.

The corner of her mouth trembled as she looked at me; I thought she meant it for a smile.

I did my best to smile at him, though I could feel the corners of my mouth tremble.

The corners of her mouth were trembling.

She managed a smile, but the corners of her mouth trembled slightly.

She was doing her best to sound in control of herself, but the corners of her mouth were trembling.

Despite her efforts, the corners of her mouth trembled ever so slightly.

Her cheek muscles twitched, the corners of her mouth trembled.

Niall grunted, the corner of his left eye trembling.