One time a coworker brought a piece of paper to my office where I sat with my back to the door.  When I turned to greet her, I was eye-level with the paper and immediately started scanning it and offering feedback.  As our conversation wound down, I noticed she was wearing a bright, yellow scarf.  What struck me was not the scarf itself, but the realization that I was many minutes into the conversation before I ever looked up at her eyes.  I had failed to acknowledge her or engage with her visually while talking!  This was a huge eye contact mistake.  What a missed opportunity to make the person feel welcome or appreciated for the work she had done.