Reference Icon (Tough Metaphor Challenge)

As part of @Denis Sazhin / Iconka.com's metaphor challenge, I was challenged by @Vadim Carazan to develop a metaphor for "reference".

Here's the challenge.

1. You can leave a comment to this post and I'll give you a tough (in my opinion) metaphor to develop.

2. You make a rebound of this post with the icon you create based on that metaphor.

3. Whoever comments you gets a tough metaphor from you, and they do a rebound of your post with their icon.

4. And it goes on till we're done playing.

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Some basic rules:

1. No text preferably. I feel like using text in icons is sort of an easy way out.
2. Keep it simple. It's supposed to be an icon, not a concept illustration.
3. Keep it civil, keep it smart.
4. I think feel free to share your variation of the same metaphor in the comments, if you want to.

Let's get that brain working!