Sometimes big chunky crumbs (really toast fragments) get lodged and the 'invert and oscillate' method fails to deliver. Then you need to unscrew the four crosshead screws located on the underside of the toaster and dislocate the entire bottom section.
This can reveal some secrets however. I have just completed this procedure and was a little alarmed to discover a thoroughly dessicated mouse in the bottom of the toaster amongst the toast rubble. Must have thought it had arrived in some kind of paradise until someone popped in a couple of slices of Hovis and slid the carriage down...
Could've been worse; could've been embedded in Breville gunge.
'Rodent Recipes' Joe, February 2008