When I am at the stand asking for a sustaining vote and any who object, I make it a point to look over the congregation thoroughly - and, for the objection part, look behind me at those sitting on the stand, as well. I just think I should do what I can to make sure everyone knows I take the time to look and grant the possibility that there might be someone who would object.
In most situations, with most callings, the sustaining will be automatic and almost unthinking (which is not the ideal, but is what it is) - but there can be situations where someone knows something not available to the person extending the calling and hidden by the person accepting the calling, and I believe that such a possibility is important to validate in the minds of the members.
"By common consent" should not be an empty phrase.
3 hours ago