Today's violation of the Principle of Least Surprise

  var answer = [];

  for (word in ['this','language','can','bite','me']) {
     answer.push(word);
  }

Just to make it easy, I'll tell you that the language in question is Javascript, [...] is an array constructor, and .push appends its arguments to the end of the list/array. The answer, of course, is...

( drumroll... )