The question above is similar to the old "mistaken identity" argument that seems to popup every month. It came from an article posted on Occultview.com entitled, "How Bigfoot Vanishes Without a Trace".
Is it possible that some Bigfoot sightings are the result of crazy bears walking on two legs? Could bears explain the vanishing Bigfoot tracks? According to the author, it's possible that bears can sometimes play tricks on us humans by going from bipedal to all fours.
An excerpt from Occultview.com:
In seeking to discover Bigfoot, we are not looking for a beast that walks on four legs. A four-legged beast would be considered a bear or a moose. Imagine spotting a Bigfoot and afterwards only seeing an animal scampering away on four legs. That animal could not possible be Bigfoot?
The idea of bipedal animals with human-like characteristics is universal. The children’s story of Goldilocks and the Three Bears contain what we would call Bigfoot characters. Little Red Riding Hood’s Big Bad Wolf is a man/beast. The legend of the werewolf is exactly about a combination of man and animal.
We assume Bigfoot is an undiscovered hominid because it walks on two legs. Without any clear and undisputed photographs of this beast, we are assuming it is a hominid because it makes sense. What if there were some bipedal bears suffering from a strange compulsion to walk upright? Call it a bipedal mental illness. When disturbed the animal flees on his four legs and Bigfoot vanishes.
Searching for such a creature…they would seem supernatural. When walking upright it was a two-legged man-beast, but on four legs it is a natural creature…not worthy of attention. Looking for Bigfoot, we’d just see a scampering bear. Could Bigfoot be a bear with a mental illness?
Read the full article here.