Revealing mistake: When Robin storms into her room with her gun, she slams the door and the entire wall shakes. (00:20:00)
Continuity mistake: When Ted, Barney and the girls are heading to the South Bronx in the cab, keep watching Colleen's head, near when Barney says, "Somebody's been watching too many Seinfeld reruns", her head moves instantly between shots, from looking towards Ted to looking at Barney.
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 ★