Clifford D. Simak Quote

What your friend told you of his seeing of the time wall is true, Henry said in Boone's mind. I know he saw it, although imperfectly. Your friend is most unusual. So far as I know, no other human actually can see it; although there are ways of detecting time. I tried to show him a sniffler. There are a number of snifflers, trying to sniff out the bubble. They know there's something strange, but don't know what it is.

Highway of Eternity (1986)