Revealing mistake: When Katniss is blown back from the explosion, her stunt person is visible. This can be proven because the stuntperson's skin tone is different and her hair is not in a braid. It is in a ponytail. Wires can also be seen pulling her to give the illusion that she was blown back from the explosion. (01:33:00)
Revealing mistake: Katniss shoots and kills someone who throws a spear at Rue. When Rue says "you have to win" we see a shot of the dead bloke with the arrow sticking out of him. In this shot, if you look carefully you can see a square outline under his shirt that the arrow is stuck in. (01:36:20)
Revealing mistake: When Katniss is running from the fire bombs, when she lunges forward, you can see her stunt double's face.
Chosen answer: The tributes could not take anything in with them, but the arena is filled with different types of weapons and tools, if they can get them. Rue was clever and agile, and she could have found or stolen the slingshot or the tools with which to make one. Also, anyone, for a price, can send "gifts" into the arena to sponsor a favorite tribute.
raywest ★