Write the next sentence in the following story.

How to patch a leak in an air mattress
Know that all air mattresses lose air naturally.
Before you decide to strip the covers off of you mattress and search for holes, know that no air mattress holds air indefinitely. You will naturally have to re-inflate your mattress whether or not you have a leak.
Cold air, for example, causes your mattress to shrink. As the house cools down at night, your air mattress will likely soften a bit as the air cools.