Continuity mistake: At the courthouse, we see Marshall, Lily and Barney walk around the corner towards the bench twice, from two different angles.
Continuity mistake: At the courthouse, when Lily is eating red licorice from the vending machine, the piece she is eating gets longer between shots.
Continuity mistake: When Marshall and Lily approach the reception desk at The Wedding chapel, Marshall's cocktail moves from his right to his left hand instantly between shots. (00:07:55)
Answer: After running the marathon for Marshall with no training, he's allowed to ride the subway for free. While sat on the train, the muscles in his legs start to seize up after the marathon to the point it is painful to move his legs. This is why he can't move them. It's the same reason your body aches after a good session at the gym the day before.
Ssiscool ★