Level 97

What's up with those black tar bubbles counting down? How do I stop that? Thanks

As long as there is at least one bubble directly below a counting-down sludge bubble, to its left or to its right, it will advance down on the turn after the count reaches one. If there are bubbles below it both to its left and to its right, the direction it will go is random.

Things that will stop the advance of a sludge bubble include:
- having no bubbles directly below it to advance to
- having only other sludge bubbles directly below it (sludge can't advance into other sludge)
- having only snow-covered or ice bubbles below it (sludge can't advance into an ice bubble or a snow-covered bubble)

Once a counting-down sludge bubble stops counting (because it can't advance), it will not resume counting later, so you can safely place bubbles below it after the count has stopped.

You can try to redirect advancing sludge. For example, if there is a baby below it to one side, and nothing to the other side, you can throw a bubble to that empty side to try to coax the sludge to go that way instead, protecting the baby. The sludge advances randomly, though, so there is no guarantee that this would work.

Sludge trapped behind a chain will not start counting down until the chain is cleared. In the case of Level 97, for example, the sludge in the second stage will not start advancing until you pop the lock at the top of the first stage. So it may be a good strategy to try to clear out important bubbles in that first stage before popping the lock.