Maggie and Milly and Molly and May Horrible Thing

The "horrible thing" that chases molly isn't given a name, but we can figure out that, since it runs sideways blowing bubbles, it's most definitely a crab. But why doesn't the speaker just call it what it is? Maybe the ambiguity here is supposed to leave that "horrible thing" open for interpretation so that we can imagine any possible creature or situation that could scare our own socks off. Since molly can't make heads or tails of it, we get to feel her horror in the same unfamiliar way that she does.

• Lines 7-8: Life's full of potentially scary things. What makes those things (like a crab) even scarier is the fact that we usually can't understand what it is or why it's chasing us. Molly finds herself in just this kind of situation. She's got this bubble-blowing creature chasing her for reasons unknown while everyone else gets to have fun with shells as starfish. Poor molly.