Squirrels build nests that look like a ball and are not open (don't know the English word for it). The comic shows a bird's nest.
They are called drays. Squirrels, even though you see them chasing and fighting each other during the day, are actually quite communal in that they'll sleep together for warmth. This leads to a build up of fleas. To deal with this they usually have a number of drays on the go and vacate the ones that have too much flea activity.
One of the lard arses that populate my garden.
Squirrels also have a large, bushy tail, so I don't know what that comic is supposed to be showing.
I wonder why people crop the sources, what's the point? (I doubt OP here is the one, probably found it like this)
What a contrived set up to simply draw a gyatted squirrel. Just open up a secret tumblr account or whatever people do now and directly draw cheeked-up furries.
Why was that so funny? I mean it was very funny but I don't know why ;)