You are so right about muskrats, John. They are extremely deep animals. Hamsters are far less complex. The obvious sunny, open, guileless innocence of the hamster is the main reason that causes serious songwriters to avoid hamster metaphors, specially in love songs. They're just too straighforward and cute. Muskrats are another story! I'm sure that James Joyce would have written a lengthy novel based on Muskrats, had he lived long enough, not to mention Joseph Conrad.

The lyrics in the Batman theme, as you say, are almost the height of inanity and repetitiveness, surpassed only, I think, by the aforementioned "My Baby Does the Hanky Panky" and "Bird Is The Word".

Despite this the Batman theme has remained popular with pre-schoolers to this day. It's innately hummable. And it sounds a fair bit like the old taunt "Na Na Na Na Naaaaah Nah!" which children have been inflicting on other children since pre-Cambrian times if not before. That explains its appeal to the younger age groups.