My smile faltered, not that it was very good to begin with.

His smile might have faltered, but he didn't seem concerned.

Her smile faltered for just a moment before she got it under control.

Then he looked around the room, and his smile faltered.

Her smile faltered as she looked into his familiar face.

The smile faltered as if he wouldn't be able to hold out much longer without her.

She took a deep breath, but the smile never faltered.

But her smile of welcome faltered, for he was not alone.

Her smile didn't falter for a moment, even though she couldn't possibly know who he was.

For the first time in the past several days, his smile faltered.