I think he dug the tunnel! lol I think in fact he is invincible like Michael and dug a tunnel behind the cupboard where he keeps the smokey monster (also his house pet, of course)!
Still doesnt explain the polar bears completely.. how did they get to Tunisia or island in the pacific I dont know. Maybe there is subterrenial tunnel system that connects the whole earth and they just got lost and entered the wrong one! ha!
That also explains Jacob! Oh no.. it actually still doesnt... But we will get there, we still have 3 more seasons! hihihi