Revealing mistake: Watch closely when the first two 'slaves' run for their freedom amidst flying spears. When Jaguar Paw's friend (the chunky fellow) gets speared, it is a 'through the armpit' effect. When he's gasping for breath in the next shot, the entry of the spear is actually more in the middle of his chest.
Revealing mistake: At 48:28, there's a shot of a large bird on a rock in a river, a Cattle Egret, and it flies across screen and goes out of view on the left. Cattle Egrets are originally from Europe and were not present in the Americas until around 1877. (00:48:25)
Answer: It's a sign of the warrior passing over to death. When the warrior removed Jaguar Paw's necklace just before setting him free, it was a way of telling him that his life was going to be over soon.