1) We don't know. 2) Makes for a cool story. 3) He got a BB in his eye as a child. 4) It symbolized the blind mind dependent on its guidance from the intellect, (the intellect being either guided by the senses or the soul. The intellect is the charioteer, the mind are the reins of the horses, the horses the five senses, and Krishna symbolizes the soul).
Since MMY doesn't tell you in his Gita, here's the answer, if you haven't read this book you haven't really read the Bhagavad Gita. http://www.amazon.com/gp/reader/0876120303/ref=sib_dp_pop_ex?ie=UTF8&p=S01F#reader-link http://www.amazon.com/God-Talks-Arjuna-Bhagavad-Gita/dp/0876120303/ref=si3_rdr_bb_product
