If you are going to dunk on birth, make sure the mycelium has fully encapsulated the cake, inside and out. If the outside is covered and the inside remains undeveloped the water will fill the inside up more rapidly than the rest of the cake. Because of this the inside will expand and the cake will burst, thus leaving you with a fat crack along the side for ugly contams to infiltrate the inside.
I just recently experienced this. I knew it was going to happen as soon as I dunked it in the water and I saw O2 bubbles rapidly escaping the inside of the cake, then sure enuf 12 hours later the top of the cake had a 1.5 inch crack that wasn't there before.