(chieflyUS,idiomatic) To experience heightened anticipation or to act with renewedspeed or energy as one approaches a destination, goal, or other desired outcome, like a livestock animal at day's end returning to its barn.
1996 Aug. 11, Ian Fisher, "To U.S. Troops in Bosnia, Home Looks Closer," The New York Times, p. 18:
"The horses smell the barn right now," said Capt. Clark D. Carr, the battalion's Protestant chaplain, who knows perhaps better than anyone how badly they want to leave.
"I visualize the finish line to keep going—like the horse smelling the barn—and try to finish as strong as I can."
2001, LtCol. Bryan P. McCoy, "Identify and Combat Five Treacherous Phenomena," Ground Warrior (Summer), U.S. Navy Naval Safety Center (retrieved 14 June 2007):
Smelling the barn can result in driving too fast, not clearing weapons properly, and bypassing ammunition-recovery procedures.