I've made 2 different objects at the first time which were 'Body' object and 'Horn' object. And they've already had same Mirror Modifiers of Y Axis, Clipped.
Now I Joined 2 objects to use Ctrl + J. (Horn to Body.)
I Selected 2 vertices from the top of the head like the second picture on the below, press W to tried merge those at the center. But it's moving on to 'Center of the Head'.
I searched on the Google and Blender Manual to solve this issue without question but unfortunately, I still can't find it.
Could you please give me any solutions?