Nice game! I'd probably play this on my phone on the train if it was available on mobile. The UX isn't optimal but the fun of the game and the Dude Perfect factor makes up for it.
I think the placement of the string could be improved by setting the endpoint when the user clicks down the mouse button and showing a "ghost" of the resulting string when the mouse button is held down. Then when the mouse button is released the ghost line is created. (idk if that made sense, but the main point is that it could be more intuitive)
Overall, though, very fun game! Best one so far! Also, props for not making a spider-based game :)