(Part II). Larry Niven's Mistake.

"What’s the point of it?"
"It ends the trip. It sets me right again."
"Will it clear your head?"
"Of course!" Kthistlmup let him go and watched as he swallowed a large oval pill. "It's for cases where an asteroid comes barreling toward you. It puts me in a position to quickly recalculate my course," he explained. Kthistlmup anxiously scrutinized Barnes's mind, which was beginning to clear. In just a moment, he would no longer be able to hide what he was thinking. It didn't matter anymore whether he was willing to answer or not. All Kthistlmup had to do was read the mental images stimulated by his questions. Barnes's mind cleared further... and Kthistlmup suddenly found himself fading away like mist in the sun. His last thought was that it had been a perfectly natural mistake.
Original title: Mistake - © 1976 Random House, Inc.