#111######
#222##22##
#33333333x<- block removed from here
##########

#111######
#222##22##
#3333333x1
##########

#111######
#222##22##
#333333x11
##########

#111######
#222##2x##
#333333333
##########

#111######
#222##x2##
#333333333
##########

Now, consider moving to the last block not allowed.

Consider it a 3D case with a depth of 2. We're now at this situation.
Note the additional blocking ## in the second depth plane.

z=1         z=2
#111######  #111######
#222##x2##  #222##22##
#333333333  #33333##33
##########  ##########

#111######  #111######
#222##22##  #222##x2##
#333333333  #33333##33
##########  ##########

#111######  #111######
#222##22##  #222##2x##
#333333333  #33333##33  
##########  ##########

Now there is nowhere to go, without going to an already visited block,
but the pressure calculated in here from neighboring blocks is >= 2,
so it is not the final ending.

We will back up to a state where there is somewhere to go to.
It is this state:

#111######  #111######
#222##22##  #222##22##
#333333x33  #33333##33
##########  ##########

Then just go on, avoiding already visited blocks:

#111######  #111######
#222##22##  #222##22##
#33333x333  #33333##33
##########  ##########

#111######  #111######
#222##22##  #222##22##
#3333x3333  #33333##33
##########  ##########

#111######  #111######
#222##22##  #222##22##
#333x33333  #33333##33
##########  ##########

#111######  #111######
#222##22##  #222##22##
#33x333333  #33333##33
##########  ##########

#111######  #111######
#22x##22##  #222##22##
#333333333  #33333##33
##########  ##########

#11x######  #111######
#222##22##  #222##22##
#333333333  #33333##33
##########  ##########

"Blob", the air bubble finally got out of the water.
Then return recursively to a state where there is air next to water,
clear the visit flags and feed the neighbor of the water recursively
to the algorithm.

#11 ######  #111######
#222##22##  #222##22##
#333333333x #33333##33
##########  ##########

#11 ######  #111######
#222##22##  #222##22##
#33333333x3 #33333##33
##########  ##########

...and so on.