The "umwelt" is the slice of an animal's ecosystem that it can sense. The rest is invisible....
SUM at the Royal Opera House
SUM has been turned into an opera at the Royal Opera House in London (Composer: Max Richter, Director: Wayne McGregor). The London Evening Standard hails the opera as "immersive, meditative and sweetly fascinating". Read about the background of the collaboration in Wired.
Sum #2 book in UK
In September, 2009, Sum became the number 2 book in the United Kingdom on Amazon's bestseller list, only behind Dan Brown's Lost Symbol.