I didn't notice the bloody arms the first watch-through but i caught it the second time. He's only bloody the first time you see him when Locke is with Richard (about 9 mins in), which is odd timing. You see him *immediately* after Richard denies Locke's request to join forces with him. It's almost like Richard's faith restored Jacob, or Jacob was there to show support for Richard and to get Locke to back off.
Locke sure as hell seemed shocked to see whoever the boy was, and seeing him seemed to push him toward whatever his end goal is with even more haste. That is what made me think he has only a small time window to accomplish his task (getting off the island) before Jacob can fully recover (if the boy is Jacob.)
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