Number line: Ok, the 0 is like the flipping point but, big deal,
   you can also spin the number line around and make the positives
   into negatives, and the negatives into positives.* You just have
   stick the whole thing on a pin with the zero in the middle, spin
   it until it faces the other way and boom - -1 becomes +1, -1000
   becomes 1000 etc. Trifoil is different.* There's no point of
   balance like that... you can't spin it around to make it into
   its opposite because the opposite is always different. If you
   want to turn your left hand into your right hand, you'd have to
   turn one of your hands inside out. But then the inside of the
   skin would be on the outside, and the outside of the skin on the
   inside, so even in that case, one didn't become the other.