That's pretty much it.  When wrens (or most any smaller bird) puff up in the winter time, they look like fluffy tennis balls with feet (and tails). Okay, wrens may be a bit smaller than tennis balls.  And, I'm sure they wouldn't bounce very well.  Not that anyone would try to bounce them understand.  It's just that the bouncing sort of goes with the tennis ball analogy.

There are a pair of wrens that hunt for food on the live oak trees near our deck.  The deck is built around one of the large live oak trees.  Sometimes the little wrens will hop down the bark of the tree and disappear under the deck.  A short while later they pop back out.  They are such perky little birds.  They hop around with great animation.  Their song is noticeably true and clear - and loud.

When the wrens are fluffed up as they are in these pictures, their little faces look sort of pinched in from the sides.  It's tough when people photograph you then analyze every detail about you.  Augh.  This makes me wonder if their faces look this way on warmer days too and I just never noticed.

Yes, you're right.  They were (and still are) doing perfectly fine eating the suet from the feeder box.  But it was still fun to do.