gistfile1.txt

scala> val kidsNames = List("John", "George", "Victor")
kidsNames: List[String] = List(John, George, Victor)

scala> val beatlesNames = List("John", "Ringo", "Paul", "George")
beatlesNames: List[String] = List(John, Ringo, Paul, George)

scala> kidsNames.intersect(beatlesNames)
res2: List[String] = List(John, George)
// Looks reasonable!

// But what if we do...

scala> val beatlesNames = List(Option("John"), Option("Ringo"), Option("Paul"), Option("George"))
beatlesNames: List[Option[String]] = List(Some(John), Some(Ringo), Some(Paul), Some(George))

scala> kidsNames.intersect(beatlesNames)
res1: List[String] = List()
// Boom, silent failure