2. We can clean leaves of a plant with them.
3. We can clean furniture which made of wood with them.
4. We can wipe a CD with them.
5. We can clean ink on someone's skin with them.
6. We can apply them on our skin when we are bitten by mosquito.
7. We can gather flies with bananas and then we can throw it away.
These two men are friends, and the man with beard is maybe grew up with bananas in tropical place, so he know lots about bananas because he used to play with them since he was a child.
By the way I didn't know "banana farm" means 精神病院.
