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Just like both The Avengers and Thor: The Dark World, Captain America: The Winter Soldier is yet another Marvel Studios film with not one, but two post-credits sequences. According to Comic Book Movies source, the first begins with Baron Von Struker (Thomas Kretschmann) walking into an underground lair where he is keeping two recognizable characters hostage: Quicksilver (Aaron Taylor-Johnson) and Scarlet Witch (Elizabeth Olsen). Demonstrating their special gifts, Quicksilver is bouncing all around his cell at lightning speed, while Scarlet Witch is putting together building blocks with his mind. Von Struker then reveals what may be the replacement word for "Mutant" in the Marvel Cinematic Universe: "Miracles."
The second scene, which is after the credits have completed, is more closely tied to the actual plot of Captain America: The Winter Soldier. The sequence has the Winter Soldier (Sebastian Stan) walking into the Smithsonian Museum in Washington D.C. Going up to an exhibit dedicated to Captain America, he sees a photo and the name "Bucky Barnes" and comes to a realization. If you are really dead-set on ruining the next Marvel movie for yourself you can head over to Comic Book Movie for the full context of these scenes.