Ready? Sangreal came from the French Sangraal, then split into two words: San Greal, which translates to Holy Grail, instead of Royal Blood.
It's like a historical game of telephone.
Wait, though, Sophie thinks. Isn't the Holy Grail a cup, the one Jesus drank from at the Last Supper?
Nope. The "chalice" in the Grail legend is an allegory; a metaphor for something way more powerful.
Langdon's feeling smug, because this is exactly what his most recent manuscript is based on. He reflects on how shocked his editor had been when he'd delivered his theory that the Holy Grail is a symbol, not an item.
His reverie gets interrupted by Sophie yelling at the taxi driver to drop his radio mouthpiece.
She grabs the gun out of his pocket and holds it to the driver's head.
They abandon the driver in the Bois de Boulogne, with Langdon driving, even though he has no idea how to drive a stick shift.