Personality traits associated with finishing other people's sentences? I read in a North American undergrad psychology textbook, that people who tend to finish another's sentences tend to be emotionally intense. I think "emotionally intense" is the wording that they used. The impression that was given is that the type of person tends to swing moods more often or to a larger degree; they're more emotional.  

Can someone cite the study? And does anyone know any other traits of people who like to finish another's thoughts?
Several factors may influence a person to finish off other peopla's sentences.
- The person may be stressed (and some people stress more often than others, thus stress may cause some people to do this more often)
- ADHD is said to cause an impatience, making the clients finish off other people's sentences:
http://www.healthline.com/health/adult-adhd
- A person may have a lot of energy, spending a bit of this energy on finishing off other's sentences.
- The speaker and the listener might ble close to eachother, and know eachother very well, maybe the listener was "just thinking of just the same thing"..

Whether or not I can find sources on "emotionally intense" people doing this, depends on how one defines being "emotionally intense". You could probably call any of the above examples emotionally intense people...