Thanks Andy! I love this discussion!
I can explain more here by why I think this isn't much of a ripoff. The big thing in my book is context. In terms of context, you have a monster under the bed. The bed is made for sleeping at night. People snore at night. So it's not a big stretch to think that the idea of the monster snoring loudly would be a logical choice by anyone drawing a story about a monster under/in a bed at night.
With a real infringement case, it would need to be something that ISN'T linked by logical conclusion or context. For instance, If the monster took the kid to Las Vegas to gamble. That (albeit insane) idea is very specific and non linear in terms of what people think of with monsters under the bed story. So if two artists had a monster taking a kid to vegas, then we have a real case of plagiarism or influence.
So the idea of a logical (or generic) conclusion vs. a specific creative choice or detail makes a big difference. Does that make sense?
To add to this, the character design can be broken down in the same way. Things that are inherent in monster design: Horns, claws, fur, fangs, etc. Colors vary, but are typically very standard yellow or blue, or green, etc. So we have two pretty predictable monster designs here. But they actually aren't that similar. If we were to break down specifics (as applied to infringement) it would go something like this:
Are items similar?
Color: Yes (generic)
fangs: sort of
drawing style: no
So you can see there are more "no" answers here than yes answers. Now, if we are talking unexpected and specific, you would have a different story. For example, If the character was blue with polka dots on the arms and had red stripes on the legs while wearing a magician hat and holding an umbrella, that would be much more protected. It would be easier to make the case of infringement. So this is a way to see how close you are to someone else's work.
The other thing about thinking in this way is it stops you from worrying about other people writing or drawing the same thing as you. For example, I'm writing a story about the moon. THere are a bunch of children's books about the moon. So I need to make sure my solutions are specific and don't overlap in meaningful ways from what's out there. But the typical or generic information about the moon is available to me since that stuff is not specific to an individual story.