A note on the letters page of "The Amazing Spider-Man" #125 states: "It saddens us to say that the whiplash effect she underwent when Spidey's webbing stopped her so suddenly was, in fact, what killed her". The comic book "Civil War: Casualties of War: Captain America/Iron Man" (2007) concurred that the proximate cause of death was the sudden stop during a high-speed fall. An issue of "Peter Parker/Spider-Man" revisits the issue, and further confirms Gwen died of a broken neck due to the use of the webbing. On the other hand, in the 1987 edition of the "Official Handbook of the Marvel Universe", Gwen's death is attributed to the fall, not to Spider-Man's webbing, though the listed cause of death is still technically true - if she hadn't fallen from the bridge, the event that caused her death couldn't have happened. In his book "The Physics of Superheroes", physicist James Kakalios confirms that, consistent with Newton's laws of motion, the sudden stop would have killed Gwen Stacy.