Mersenne: filled steins

[Spike Jones]

[EMAIL PROTECTED] wrote:

Steve Harris (with Alex Kruppa for moral support and more importantly, to
run the tap and make sure the Steins stayed filled) wrote:

Since this post has nothing to do with mathematics or primes, do
post me offlist if you know the answer.

Someone gave me a german beer stein.  It has a lid thingy on it
with a thumb trigger that makes the lid pop open.  Pray tell, what
is the purpose of that lid thingy?  spike