its basically a short cut to parenting the deformer to the group node called jellyfish. Try selecting the squash node then shift select the jellyfish node and hit P to parent it to the group. Its the same as middle mousing over it. I just did both and it works fine for me

In the settings for the deformer, make sure all the settings are at default in case some is amiss as maya can be a bit strange sometimes.

hope this helps

Jay