The intervals between the lights were long, and a fog was thickening the whole city.

During the hours they were inside, the fog thickened.

But after most of a moment the fog thickened, becoming more like sludge.

The creature began to smoke, but the fog was thickening.

When the fog had thickened around him, he turned and ran.

If anything, the fog had thickened, so that it was impossible to see even a meter in any direction.

But only a few; they stopped, and the fog thickened about them again.

I want to go up, if you please, before the fog thickens.

The fog still held, thickened by the smoke of the barrage.

And as her guilt grew, the fog thickened - yes, why not?