Vocals are only used in episodes with hominids. In "Next of Kin", they are long wails; in "Mammoth Journey", they are shorter, word-like vocalizations. This is likely because australopithecines were not capable of speech, while both cro-magnons and neanderthals were.
The song sounding while the Smilodon pack hunts includes what sounds like swords (or you know, sabers) clashing.
If you look carefully at Half-Tooth's first fight with the brothers, you'll notice that only one of the brothers actually engages Half-Tooth with physical contact. The other mostly circles around the real fight and seems to act more as support (towards the end of the fight, both brothers face Half-Tooth, and this is when he flees). Why is that? Later the episode explicitly states that one of the brothers was dominant over the other. It's possible that the brother doing the real fighting was the dominant one, while the brother circling around was the lesser one that Half-Tooth defeats one-on-one later.
"Mammoth Journey" begins with the death of a female mammoth and (almost) ends with the birth of another one. In other words, the herd would have remained the same size if the Neanderthals had not killed another two mammoths, one of them the matriarch. This could be seen as a metaphore for mammoths only being able to reproduce fast enough to cover their natural deaths, and hunting adding a straw that will send them to extinction.
From "Saber Tooth": Half-Tooth is the "hero" of his episode simply because it takes place during these particular three months when the brothers "dethrone" him. Three years prior, he did exactly that to another male, took over the pride, and killed all the cubs that might be living in it.
Probably Blue And Orange Morality, the brothers are the villains because they double teamed Half-Tooth, instead of only one of them facing and defeating Half-Tooth, like Half-Tooth probably did to the one before him.
In the sixth and final episode, the narrator says "No species last forever," while humans walk around a museum full of prehistoric animal skeletons. Does that mean humans are next?
