i'm generating a "switch-frame" event, but have no idea how. any help?

i'm generating a "switch-frame" event, but have no idea how. any help?

[bigfaceworm]

Emacs 21.1 on Linux (running inside a vnc session, listener is on
winXP)

Every once in a while I'll be typing and doing my standard things
inside of Emacs (with two frames open), when suddenly the focus
changes from one
frame to another!  I've no idea why - I hadn't typed "C-x 5 o" or
anything.

I'm trying to figure out what I did that caused the behavior, b/c it's
really annoying.  Any ideas?

Here's my lossage:

o C-v C-v C-x 5 o a d d SPC g e t B e g i n D F S ( 
p , SPC p ) SPC t o SPC p r o v i d e SPC w a y SPC 
t o SPC i t e r a t e SPC a l o n g SPC s e m e <backspace> 
g m e n t s SPC c o n n e c t i n <switch-frame> g 
SPC C-x 5 o C-x C-g C-g C-h l SPC M-x C-g C-x 5 o C-h 

Note the <switch-frame> event.
I don't even know how to find that "key".
I swear I didn't hit the mouse and that I'm the only one
in this VNC session.

Any ideas?