So we grew together
    Like to a double cherry, seeming parted,
    But yet an
    union in partition,
    Two lovely berries molded on one stem...
    ~William
    Shakespeare, A Midsummer Night's Dream
    My sister and I, you will recollect, were twins, and you know how subtle are the
    links which bind two souls which are so closely allied.  ~Arthur Conan
    Doyle, The Adventure of the Speckled Band