Immediately before the "על חטא" prayer on יום כפור, we say a paragraph that says God knows everything. It includes this passage:
אתה חפש כל חדרי בטן ובחן כליות ולב
In my own translation:
You search all the abdomen's [or: uterus's] rooms and check kidneys and heart.
I know the kidneys are considered the seat of counsel and the heart the seat of feelings and sometimes of thoughts. (See almost any chapter of Mishle, for example.) But what does the abdomen/uterus (בטן) represent, or why do we say God searches it?