belly button
Bauchknopf is the German term for belly button. It is used in the same way as in English, referring to the small, depressed scar on the abdomen that marks the point of attachment of the umbilical cord during fetal development.
There is a lint hanging on the belly button.
The example is a straightforward sentence. Here, the subject is a 'lint' and the location of it is specified as 'on the belly button'.
He gently touched her belly button.
In this sentence, the action of touching is performed by 'he' towards 'her belly button'. The adverb 'gently' is used to describe the manner of the action.
The belly button is the remainder of the umbilical cord.
Here, a factual statement is being made about the belly button being the remnant of the umbilical cord.