But casual observers might not have even noticed the changes.

The average observer, she said, won't notice the difference.

Her hesitation was so slight, only the most careful observer would have even noticed it.

An observer would have noticed nothing out of the ordinary.

A few close observers of this column had noticed that I have barely mentioned him since his birth 13 months ago.

The amount of time wasted on them, as many observers have been noticing, is astronomical.

The uninitiated observer would not have noticed any change in that day's events.

A more critical observer would have noticed some important omissions in the book's text, however.

Indeed, the effects can be so subtle that an observer might not notice them.

They played very close, and a canny observer would have noticed that both of them were holding back a little bit.