Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: After rubbing a rubber brush on wool, Gilbert is able to use the brush to pick up small strips of paper. What causes the paper to be attracted to the brush?
The rubber brush picks up a static charge from the wool, which attracts the paper.