The Time Traveler laughed and sipped his Scotch. “Would you want to kill your grandfather?” he said. “Or anyone else?”E Rocc and SlowBoat407 are on the right track, I think. I dismissed "Grandfather" at first, thinking of it simply as a literary device for a character to generically address an old man. BUT, it would seem that the author would be younger than the grizzled, in-his-60s, time traveller. And the traveller does make repeated references to the author's grandchildren -- rather than, let's say, his children. The references suggest a close familiarity with them....“Well . . .Hitler maybe,” I said weakly.
The Traveler smiled, but more ironically this time. “Good luck,” he said. “But don’t count on succeeding.”
The ironic smile and accompanying words ("don't count on succeeding" on killing your grandfather) now reads as especially chilling to me.
I don't know what the three words are, but it seems they could have something to do with the relationship between the author and the traveller... and also words that would resonate with any other time traveller on an emotional level, according to the author. "I love you"? I don't know.
It's "Write this story."