ELI5 Balloons - why is there a ring at the opening of a balloon?

Why is there a ring at the end of the opening of a balloon? What creates the noise of a ballon popping? Who invented the ballon? Why do helium balloons shrink in size over time?

.. we explain like I'm five

Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: marv1nnn, trooper_x, secretantworshiper, fujikitakyusho, brian_vogel, 18_usc_47 and moskau50

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