Schroeder gets out of the house some. Playing ice hockey on a frozen pond is sort of a winter analogue for vacant lot baseball. I wonder how much this happens anymore.
The second time Snoopy uses his imagination leads off a week-long sequence, and I think this is the bit that really causes it to "take." They're a good opportunity to expand the character into something unique, and they have the additional virtue of making possible a lot of really fun drawings. Snoopy's open smile upon finding his victim is my favorite part of this one.
In these early strips Snoopy usually restricts himself to being some kind of animal. A rhinoceros is an interesting choice -- not a lion or a bear an elephant or something more usually recognized as a strong, powerful animal. Not that rhinos are slouches of course -- just that I'd think they would be thought of iconically by their horn, not their strength and size.
Charlie Brown seems worried that Snoopy actually thinks he's a rhinoceros. But how would he have been able to figure out what Snoopy was pretending to be?
WHOOPS! I think this is the first time Snoopy has actually attacked anyone on-panel.
Some rhinoceroses are self-conscious about their appearance. Anyway, a real rhino bump would be nothing to joke about.
Up until now Lucy's crabby personality has manifested in three primary ways: by reputation (her mother calling her a fussbudget), her dealings with Linus, and in defending her strange opinions against Charlie Brown. Here is a fourth: the bucket of cold water on Snoopy's head. It's also the first instance of her physically standing up to another character, here in the second panel.
I really love the goofy grin on Snoopy's face in the first panel.