Paradox or Riddle. Brain-training exercises.

I don't know if it will "float," physics is silent on that, but it's clear that nothing will spill. Naturally, assuming we don't throw this cup with force, causing waves to splash in all directions. The trick is that the cup, together with the bolt, cannot occupy a larger volume in the water than the volume it initially displaced, unless their average density is lower than that of water. But in this case, they wouldn't sink at all, and according to the problem, they did sink.