This refers to a state when, as shown below, there are four columns where only  can be entered.
It is a bit small, but we wrote out all possible combinations of where  could be entered below.
This is a variation. As shown below, it appears that an incomplete jelly fish arises at a relatively early stage.
In the diagram below, a jelly fish is hidden.
 is forming a jelly fish. We made all ’s blue. Can you find it?
The fourth column, in the diagram below, is a jelly fish.
Therefore, the ’s in the pink cells can be eliminated as candidates.