The BTS video include the cast and crew of TT3MD filming scenes from the film and Matthew was shown practicing on his fencing technique amongst other things. It also contains SPOILERS within (though it doesn't give away much, really...), so if you would rather not be spoiled...then, don't watch it!
If you don't mind spoilers. Then, by all means, check it out and watch it at your own risk below...
BTS Video: The Three Musketeers 3D
(source: Tailerseite.de)