Dyngus Day is a Polish celebration, held the day after Easter. As well as general merriment, boys douse girls with water, and slap them with pussywillows. Unusual indeed. Well, that is what they do, and they enjoy the event every year.
One thing We Rhinos have learned is that We will never understand every folk custom.
BTW, the Polish word for Rhinoceros is Nosorozec, in case you need it.