Someone that looks like they could potentially handle tasks on their own, be a good apprentice, and that you won't have to spend time arguing with to get them to do something simple.

Basically an intern should be a humble worker that gets the job done.

Interns come to work the first day feeling like they will be valued and a part of the team, but are hired because they are seen as cheap labor by the employer, and once they get there are usually not treated as a "real" employee. So they need to get work done, but in a way that doesn't rock the boat.

I worked a semester as an intern at a big technology company, and was constantly pleading with people to give me something to do. They usually didn't, so I ended up just reading books or writing toy programs. And then management got mad at me for not doing any real work, so I went back to everyone I could find pleading for work. And so the cycle went. I hated it, and the most notable thing I learned was that I did not want to work for that company ever again.