Always, ALWAYS proofread again after the copyeditor has been through, just in case.

Three good methods, can be combined:

1. Read it out loud.

2. Use a text to speech utility or screen reader to read it to you.

3. Read a proof copy of the printed book BEFORE it goes out. Seeing it in a different format helps.

Copyeditors are human and can make mistakes, although in this case the copyeditor should have queried, so it is very much on them.