Board Thread:Manga/@comment-24930713-20151109044731/@comment-26932251-20151128021930

Well, to say it's their only weakness might be a bit of a misrepresentation of battle doctrine.

Yes, apparently a titan can't be offed without cutting the nape but that doesn't mean that the titans don't have weak points that can ultimately aid in that final goal such as the achilles tendon or the joints or the eyes. Maybe the thunder spears are able to suit in that goal.

Also, one thing to note, Marlo says that they 'cut through titans like butter' so there has to be something more to them other than just being mere poking sticks.

My hypothesis is that the reference to lightning may mean that it uses electricity or something resembling lightning in some way possibly related to that shining oar they found underr Reiss's chapel.

Keep in mind, in theory a titan has to be killed by cutting the back of the neck but all you really need is enough force and theoretically a titan could be killed from any angle as long as the target point is damaged enough so maybe the thunder spears make things easier because a soldier can then strike a killing blow from whichever angle is the most opportune.

Judging by the 'the soldiers ready their new weapons' caption at the end of the last chapter, we're almost certainly going to find out in the next chapter.