Count number of words in a string (Scala)

This is improved snippet from Programming in Scala

def countWords(text: String) = {
    val counts = mutable.Map.empty[String, Int].withDefaultValue(0)
    for (rawWord <- text.split("[ ,!.]+")) {
         val word = rawWord.toLowerCase
            counts(word) += 1
    }
   counts
}

Returns Map form word to number of occurrences