Justice Souter writes:

The Government may say that a person "uses" a firearm simply by receiving it in a barter transaction, but no one else would. A boy who trades an apple to get a granola bar is sensibly said to use the apple, but one would never guess which way this commerce actually flowed from hearing that the boy used the granola.

  In reference to Justice Souter's somewhat unusual lunchtime habits, commenter Terrivus chimes in, "If only he had also mentioned yogurt, he would have covered pretty much everything he has ever eaten." Heh.