The DHARMA logo suggests that the bear must've been let loose during the heydays of the DHARMA initiative.
The caves are huge, connecting to the caves used in Season one by some of the castaways.
Why would The Others feed the children to the Polar Bear? This seems highly unlikely, especially since Zack and Emma have been seen alive and well in Season 3.
Zack and Emma have also appeared in Season 6, in the Temple.
An inhabitant from the Pearl tried to reach the Swan, perhaps to tell the inhabitants of the Swan that they were being fooled, but was attacked by the polar bear before he or she could reach the Swan.
The cave the polar bear inhabits was once used by humans. The entrance to the cave seems almost too well carved, especially with dimensions shown in the episode. It almost seems as if the entrance was built to allow for human entry. It also appears that there was a door already opened and up against the rock wall in one of the shots with Locke peering into the cave. This could either mean that it was an abandoned DHARMA station, a lair for The Others, or even a simple refuge for previous castaways on the Island.
One of the human skulls looks cut, with a straight edge or perhaps the polar bear's teeth.
Are the caves that are present in Signs of Life but nowhere else in the show.
The Polar Bear carried the toy truck into the cave on its own.
The skeleton partly covered by some fabric with the logo from the Pearl is that of a baby.
Could explain the toy truck.
Not likely, as the skeleton cuts short just where the waist should be. You can see the vertebra still sticking out.
The cave is the entrance to a lava tube system used by the Others for rapid transportation around the Island, the polar bear, which is fiercely territorially and infamously dangerous to humans, guards the entrance.
The tonka truck, a boys' toy, could be related to Karl's childhood on the island.
The tonka truck could be related to Annie's life on the island, even though at the time period in which her fate is uncertain (i.e., at the very least after the Purge) she would already have been an adult in or nearing her thirties, and most likely would not have found amusement in such a toy.
The Tonka truck is the Polar Bear's toy from when it was in the cages.
In "Further Instructions" Locke finds Mr. Eko in a polar bear cave that contains skeletons and a tonka truck.
Eko says, "You can still protect them. You can still save them." This is most likely in reference to keeping them on the island and saving them from their bleak futures.
The cave leads into the Frozen Wheel Chamber below the Orchid Station. This explains how a polar bears skeleton with a collar bearing the DHARMA logo was found in the Tunisian desert. Since there seems to be no way to get into the chamber without using the well, or destroying the vault, it seems unlikely DHARMA had direct contact with the wheel and used the bears to experiment on the wheel. At some point after The Purge, one or more bears relocated to the cave, found a passage into the frozen wheel chamber, and turned it. It is possible it felt like it had to turn the wheel, as a result of the mental experiments the Initiative performed on them.