Magic snap/bridge selection to selection? How is this done [video example]

You can see the modeler selecting an edge loop (or face?) then selecting a second bit and doing some menu trickery and like magic the two snap together! This is different from ‘merge at’ as that only works per vertex, this is taking in to account the original position of one of the two selected edge loops/faces and snapping the verticies of one of the two selected bits on to the second. I would love to learn how to do this! I’ve looked about quite a bit but only found some really old conversations about the possible implementation of a bridge tool back in '08.

They bridge the two selected edge loops (W / Bridge Two Edge Loops) then deletes one of them (X / delete edge loop)

Oh wow that’s odd I tried that. It seems a bit temperamental. I had some trouble getting it to work with two edge loops. Is there some sensitivity to which selection mode you’re in? I seemed to notice that it ‘did nothing’ and simply deselected the two edge loops when in vertex select mode, later it decided to work, I believe I was in edge select mode when it did.

Thanks for the reply! Now why didn’t I think of pausing the video?! *slaps forehead