It’s a very old nursery rhyme dating from 1744. There are variations, but it’s basically this:
Ladybug! Ladybug! Fly away home. Your house is on fire. And your children all gone.
All except one, And that’s little Ann, For she crept under The frying pan.
In 1982, it would have been unheard of for a pet store to be selling snakes in a window like this. Puppies, bunnies, guinea pigs, sure, but not snakes. Maybe they would have one or two in the back of the store, but it wasn’t common. That makes this scenario unlikely and somewhat absurd. Plus, Larson loves snakes and probably this would have been a wish fulfillment for him.