It's said that cutting off the end of a cucumber and rubbing it at the incision makes the cucumber less bitter. It would be very surprising to me if rubbing just one end of the cucumber could alter the taste of the entire vegetable—is there any evidence of this?
For example, this website states that you can remove bitterness by rubbing the ends of a cucumber.
Cucumbers are a healthy snack, but they often have a bitter taste. You can get rid of this bitterness by thinly slicing off both ends and rubbing one piece against the cucumber.