Trivia: Katniss Everdeen and Peeta Mellark are the only Hunger Game tributes ever referred to by their first and last names. The other tributes are just identified by their first names, even when they're being introduced by Caesar Flickerman during the televised interviews or their scores are being announced on television.
Trivia: Isabelle Fuhrman, who plays Clove, originally auditioned for the role of Katniss, but was told she was too young for the part. When she was later called back for the role of Clove and succeeded, they had to make Clove incredibly skilled with knives to make her seem just as intimidating as Cato, Glimmer and Marvel.
Trivia: This movie has approximately 1200 shots that are composed of CG animation. The director Gary Ross' previous movie, The Tale of Despereaux, was also composed of approximately 1200 CG animated shots. The Tale of Despereaux was a fully CG animated movie, yet the live action Hunger Games had just as many CG shots.
Answer: I watched this scene multiple times on YouTube. There is definitely something moving that probably is not supposed to be seen. I'd agree with your assessment that it looks like a hand. Most likely a film crew member is crouched on the floor performing some technical function during the filming. Just what it is impossible to tell. You should submit it as a "movie mistake."
raywest ★