Some processes stay active after killing its PID

[Stephen Montgomery-Smith]

On Tue, 27 Nov 2007, Honza Holakovsky wrote:

> Well, didn't know that, "/bin/kill -9 wdfs_PID" works, great
>
> Thanks a lot, after your advice I read an article about csh built-in
> commands, never heard of it from any fbsd handbook...

I am completely baffled why this worked.  Why would /bin/kill -9 work when 
the built in csh kill -9 wouldn't?