When I was in college (in the 70s) I visited the London Zoo in Regent's Park during a summer vacation. They had a wonderful indoor nocturnal exhibit, all sorts of critters in dark terrariums who were awake during visitor hours because their normal schedule was reversed.

It was, not surprisingly, dark in there. It was hard to read the labels. As I recall, there were reptiles, and bugs, and all sorts of things, but they hid in their foliage very well and half the time you couldn't tell what was lurking in the greenery.

At the same time that I entered, a young father came in, carrying his toddler son up against his shoulder so he could see into the enclosures. The two of them followed directly behind me as we circulated along the edge of the exhibit.

I learned three things that day.

First, small children have a hard time trying to see something in a darkened terrarium. As far as the kid was concerned, he and his daddy were taking a walk in a funny dark place with lots of plants. Hints from his father didn't help him (might not know enough words yet, I thought).

Then we came to the last exhibit, and I learned my second thing.  The final terrarium housed bats. I know this because one of them introduced himself, precipitously, right up against the glass.

And then I learned my third thing. A pre-verbal toddler, introduced to an unexpected face right out of hell, has a scream of absolute outrage that is unmistakeable.

(And it's downright philosophical, an expression of extreme disapproval that such a thing should exist in a well-ordered universe, a betrayal of all that is sane and just.)

So surprise your readers and get their attention. Then never let it go.