killing threads == expunging?

[David Cohen <dnc@bigfoot.com>]

A while back there was an informative thread about the difference
between marking a message read and expunging it.  This prompted me to
add the following to my .gnus:

(define-key gnus-summary-mode-map "d" 'gnus-summary-mark-as-expirable)


But now I wonder about other ways to mark as read.  In particular,
killing a thread with ctrl-k.  Will that expunge articles or merely
mark them as read?  And is the behavior configurable?

Thanks.

-Dave