I created a scenario in the editor that I was using to mess around with the various AP mines that were included with the alpha launch.
The scenario consisted of Me and about 8-10 OPFOR units that were to close on my position and be blown to bits by the aforementioned mines. Things were progressing well however several enemies managed to breach my defensive perimeter.
I was in deep trouble. I ran to take shelter in a nearby house and began exchanging fire with my battle hardened foes.
When I inevitably had to reload I noticed out of the corner of my eye that the door to the shack had swung open. "This is it..." I thought to myself as I awaited a grenade or enemy rifleman but nothing came...
I sat there for a couple of seconds and then I saw the snake slither into the shack with me.
"Mind if I hang out in here with you, buddy? It's scary out there..."
I haven't been able to reproduce this yet as I haven't really tried but it appears that snakes can open doors.
If it turns out to be a non-issue/never gets fixed I'm perfectly fine with snakes being able to transcend the physical limitations that a creature without any arms or legs would have with being able to open doors.
ArmA III is turning out amazing so far - Keep it up, gents!