Great observations everyone, glad I got so many answers so quickly!
Which Gems? Crap! I should have jotted down which of the older ones mentioned the mouse when I first listened. I thought it appeared in "Power Pop Pop Pop", from May 2007, but I just checked and it wasn't there. But almost all Gems posted so far are 3 years old or older, so if I discover an old reference I'll return here to post it. It seems that the mouse-wearing-a-cape bit has been around longer than the last couple years, but only reappeared periodically. Lately they've used it more often.
Although I think Mr. Spacely has a good theory:
I love when Wursterisms stack. Like, a normal reference to GG "passing on" will cause him to laugh, which will then cause him to break out the "mouse in a cape just ran by," which will cause him to laugh more, which will then cause him to mention the pollen.
Perhaps the mouse bit is just what he says when he's about to laugh; and of course that can cause the jokes to "stack". That's happened to me many times!
Matt from Springfield [Virginia]
