Like when you have a retarded bond that decides to jam itself into an unsaturated alkene. A bit like that relative you never liked.
This happens in some stupid stages you're meant to remember. As if it'll mean anything to you in life.
Stage number one. The retarded bond ATTACKS the chilling alkene.
As the chilling alkene gets shanked by the retarded bond, one of its bonds snaps off. The electron's left hanging there.
As the bond's snapped off, the retarded bond makes advantage of this via exploiting the open port, as the following diagram illustrates.
And then we get this:
So, we end up with this: