The dogs zero in on the treat in my hand.
zero in
idiomTo converge (on).
Origin
disputed originThe phrase possibly comes from adjusting a sighting mechanism of a firearm to minimise the discrepancy between where the sight points and where a bullet lands on a target. Another possible source is the Cartesian coordinate system in mathematics. In the coordinate system, points are defined relative to an origin (point of reference) labeled O, which has an (x,y) coordinate pair of (0,0).
As the deadline approached, the team zeroed in on fixing the most serious bugs first.
With the evidence mounting, the detective's attention zeroed in on the quiet neighbor who had seemed so helpful at first.