You can pose unanswerable questions that leave creatures momentarily dumbfounded as they dwell on their significance.
If the creature fails its check*, you choose whether it loses its next action or you gain a +2 bonus on all damage rolls you make against that creature for 1 round.
GMs may wish to reword the text of the second sentence as:
“The target may attempt an opposed Sense Motive check, and if the creature fails its check…”
Sean K Reynolds wrote: Bluff is always an opposed check against the target’s Sense Motive check. If the target fails, it loses its next turn.
Pathfinder Companion: Gnomes of Golarion. Copyright 2010, Paizo Publishing, LLC; Authors: Hal Maclean, Colin McComb, Mark Moreland, Jeff Quick, Sean K Reynolds, Steven Schend, and Owen K. C. Stephens.