Seam Ripper

A good seamstress is best friends with her seam ripper.  Not because she can't sew, but because she's probably a perfectionist.

Seam rippers, like other sharp tools, get blunt.  Don't spend lots of money on fancy seam rippers, buy small inexpensive ones and change them often.  You'll notice the difference.  A sharp seam ripper will 'rip' seams quickly, efficiently, and cleanly.  A blunt seam ripper will not.

Make sure you have a sharp one!