Sandra Bullock -- Anatomy of a Surprise

6/7/2010 4:20 AM PDT

Sandra Bullock -- Anatomy of a Surprise

How did the producers of the Spike TV Guys Choice Awards keep Sandra Bullock's surprise appearance under the radar? Tiger cages. Yes, really.

Sources tell TMZ the plan for Sandra to appear was weeks in the making and kept under tight wraps. We're told Sandy didn't think twice once she heard it was an award selected by the troops.

As for the logistics, live tigers were part of the awards show (see above) and we're told the cages were purposely placed to keep Sandra's entrance as secret as possible right up until she walked on stage. Siegfried & Roy would be proud.

You can see the tigers -- and Sandra -- June 20 on Spike TV.