During the wood chopping scene, after Fitz and Olivia's talk, Fitz sets up a flat piece of wood with a large amount of exposed interior wood. When he swings the ax, the wood has become a cylindrical piece with almost no exposed interior.
President Grant misstates how the 25th Amendment works. He would not need VP/Acting President Langston's acceptance of his reinstatement letter. Instead, his reinstatement would be automatic upon his presenting of the letter to Congress. Langston could thwart him by taking action, along with the Cabinet or Congress (presumably the same group who originally supported Langston's move to become Acting President), to deny the reinstatement; this maneuver would be difficult and politically dangerous for Langston to pull off.