Harry, using his will power, forced "beads" of light that were forming along the thread back into Voldemort's wand. This caused priori incantatum, the effect that causes a wand to go back through all its most recent spells, to happen. The priori incantatum effect made "shadows" of Lord Voldmort's most recent victims, Cedric Diggory, Frank Bryce (the Muggle gardener who overheard Voldemort and Wormtail), and Harry's parents to come out of his wand. They circled Voldemort, holding him back so that Harry had a chance to direct his wand away from Voldemort's. This broke the connection in a similar way to breaking eye contact. Harry then ran for the Portkey and took Cedric back.
Sorry for the overly detailed answer. I wasn't entirely sure what you meant.