How language gives your brain a break(newsoffice.mit.edu)

  * + 1 2
    - * + 3 4
        + 5 6
      / 7 8

      1 2 +
  3 4 +
  5 6 + *
    7 8 / - *

    1+2
  *     3+4  
      * 5+6       
    - 7/8

    Recursion in Language  (p. 138):

    Our mental stacking power is perhaps slightly stronger in
    language.  The grammatical structure of all languages involves
    setting up quite elaborate push-down stacks, though, to be sure,
    the difficulty of understanding a sentence increases sharply with
    the number of pushes onto the stack.  The proverbial German
    phenomenon of the "verb-at-the-end", about which Droll tales of
    absentminded professors who would begin a sentence, ramble on for
    an entire lecture, and then finish up by rattling off a string of
    verbs by which their audience, for whom the stack had long since
    lost its coherence, would be totally nonplussed, are told, is an
    excellent example of linguistic pushing and popping.  The
    confusion among the audience out-of-order popping from the stack
    onto which the professor's verbs been pushed, is amusing to
    imagine, could engender.  But in normal ken German, such deep
    stacks almost never occur-in fact, native speaker of German often
    unconsciously violate certain conventions which force verb to go
    to the end, in order to avoid the mental effort of keeping track
    of the stack.  Every language has constructions which involve
    stacks, though usually of a less spectacular nature than German.
    But there are always of rephrasing sentences so that the depth of
    stacking is minimal.

    Der Mechaniker,
        auf den wir wegen dem Unfall,
            den wir,
                bevor wir die Stadt,
                    die im Norden liegt,
                erreichen konnten,
            hatten,
        gewartet haben,
    ist endlich angekommen.

    The mechanist,
        for whom because of the accident,
            which,
                before the city,
                    which lies in the North,
                we could reach,
            we had,
        we have waited for,
    has finally arrived.