A sudden understanding, a pity mixed with horror, welled up...

A sudden understanding, a pity mixed with horror, welled up in Bilbo's heart: a glimpse of endless unmarked days without light or hope of betterment, hard stone, cold fish, sneaking and whispering. All these thoughts passed in a flash of a second. He trembled. And then quite suddenly in another flash, as if lifted by a new strength and resolve, he leaped.