I don't get all the problems from Walter's crossing over, he crossed over 2 times that I can remember, the first time to save Peter and the last time with Olivia and Co. Was Bell crossing over a lot to make for all the holes in their universe? Example of the giant hole in the river. Why do they need to seal all of the crime scenes from the bank robber? That isn't from crossing over, the guy is from the alternate side. Also, why wouldn't there be holes from the alternates crossing over to our world? Maybe because the ability to was created on our side?