An older nun and 3 younger nuns were out riding their bicycles one day when they turned down a back street made of cobblestones. As they rode down the street, the younger nuns started giggling. The older nun turned to them and said "Ladies please, remember that you are nuns."
The younger nuns composed themselves, but after a few minutes began giggling again. The older nun said again "Remember that you are nuns".
The younger nuns quieted down, but again after a few minutes of riding they began giggling again.
The older nun stopped her bicycle and said sternly "Ladies, if you don't stop all this giggling...I will have to put the seats back on!"