Oxo are stock cubes, which are broken up and used as flavouring in meals or gravy.
Bovril is a thick, salty beef extract used for the same purpose.

The joke here is a play on the different meanings of the word stock.

(This comment was modified on Oct 02, 2008 07:31 AM)

Thanks!

And, One can take stock in Bamber's knowledge

And, One can take stock in Bamber's knowledge

(this comment was modified at 07:09AM)