While running the Parasitic Pilgrimage mission for the "Of Queens and Worms" quest, I reached Mara Sov near the end while carrying the worm. I dropped the worm as I got to Mara, but then the mission let me "place the worm" even though I wasn't holding it. The mission continued, though the worm I had dropped never disappeared. It turns out, if you drop the worm before you place the worm, the timer continues to count down and kills you once it ends even if Mara begins the ritual.