Is that really the only third option? Why not a demon, or a time traveler, or a secret CIA experimental hologram, or alien UFO pilot, or...? Once you open the door to things which are not known to exist and for which there is no evidence, the options seem to extend well beyond the one you picked.
Bigfoot might not be from these parts…
The idea that Bigfoot is a yet-to-be-discovered North American bipedal ape is hard enough for most people to believe, but to imply that the big guy is really an alien makes it even harder for people to fathom. But, if you think about it, the idea that Bigfoot is an alien, with glowing green eyes and Green luminescent blood, actually simplifies the Bigfoot mystery!
A WORLD IN NEED
When the military recruits Amy Rush, a nymphomaniac who craves fulfillment, to seduce and sleep with extraterrestrials in order to acquire their technologies, they know they're getting more than they bargained for.
A WOMAN WHO NEEDS IT
Amy loves the planet (hey, she's loved a lot of the people on the planet) so she's excited to try and help save the world, and if it means she gets laid by Bigfoot, she's willing to take one for the team. Or take two. Or three. Or, well, however much Bigfoot is willing to give. Of course when it comes to Bigfoot, his feet aren't the only big appendages.
This short story clocks in around 4900 words, and was designed to be read with one hand free.