I recently read a report on a study about when babies learn to detect danger (and its correlation with the development of locomotion). According to the study, when threatened with looming objects, babies develop the same kind of neural activity as adults around the time that they learn to crawl.
When I first read the report, I imagined the conversations the researchers must have had when designing their study. First, they had to choose a looming object, and then they had to figure out how to threaten babies with it. I was also fascinated by the idea that we don't develop the ability to notice we're about to be flattened until we can do something about it.
Elizabeth does seem to acknowledge dangerous situations - pausing to register things hovering over her head, cliffs, etc. However, we can't help but notice that while her ability to detect danger seems to be developing just fine, her desire to reach the shiny usually overrides any sense of caution. Good thing she's not that fast yet!
Oh - and in case you are wondering, Uncle Dave and Brendan were building a bedframe. No comment on the balcony bonfire...