What, with a sharp sound, sends thousands exploding forward, or just a pair diving into the water?

More than twelve eyes witnessed the event, yet only two people were present; how is this possible? Solve the riddle → Our internal purification plant quietly filters toxins without asking for a raise. Solve the riddle → I am a burden that lightens when you share me, but I die when everyone knows me. Solve the riddle → What was once criticized as an ugly construction, but is now an iron monument that breathes with the seasons? Solve the riddle → Its short borders enclose art treasures and an undeniable spiritual leader, in the heart of an eternal city. Solve the riddle →