Bubbles in a cup of coffee why does this happen?

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Main Question or Discussion Point

So I just sat down at my computer with a cup of coffee before I start doing some work.. I noticed that when I dip the tip of my pencil (it is a mechanical pencil with a plastic end) in the coffee, bubbles are attracted to the tip of it.

Literally, I can put the tip up to 1cm away, and the bubble will accelerate to the tip.

Any ideas why this could be? I'm thinking it's probably due to surface tension, but I can't really remember how surface tension works.. come to think of it, bubbles always gather at the outer rim of the coffee surface - around the sides of the mug. I'm guessing this is the same effect?
 

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