Because I got `undefined` in `while (tokens[index].text in filterOut)` as I mentioned in #840. And it also seems the right thing to do: suppose you have an array of tokens, and the text of the last token is in `filterOut`. Then you'd `splice` away that last item, loop, and find yourself accessing an item past the end of the `tokens` array. Obviously not the intended behaviour. Perhaps another solution would be turning that `while` into an `if`, since you iterate over every token in any case.