Yes, it's a real Welsh folk song. It's called The Ash Grove. That's verisimilitude, bitches! Also, the lowbrow quality of popular entertainment in the Middle Ages is pretty accurate. Henry II (Richard the Lionheart's father) granted an inheritance to a jester who performed the king's favourite routine, described as a leap, a whistle and a fart. His descendants were entitled to the estate, provided they could reproduce the act. Who says history is boring.