The Animatrix has both prequel stories, as well as concurrent stories to the Matrix. One of the stories even becomes explicitly canon when the protagonist of it becomes a minor but important character in Revolutions.
The story itself takes place between The Matrix and Reloaded.
There is no spoilers for Reloaded or Revolutions in any of the 9 short films.
There's a couple ways to interpret this scene.
The straightforward approach is to just assume she was cutting her hand with the can to see if maybe the 'power' they thought they had had to do with the can or with themselves, meaning maybe only organic matter (bodies, blood, etc) will work, but the blood still dripped to the ground.
The other more ...
The Animatrix serves as a canon source of information about the Matrix World. It contains history of the Matrix - the rise of machines, the war, and why the Matrix came to be created, and humanity enslaved. The others detail the world of humans - both in Matrix and outside. Some show how some humans reject the matrix at a subconscious level - and how the ...
The Animatrix provides a deeper background in the world of the Matrix. It shows how other people experience the Matrix.
I don't think there are any (major) spoilers. There are definitely references though.
The Animatrix will definitely improve your understanding of how everything is tied together.
If you watch the film carefully, you see that the can came from the "glitched" area and bounced out of quarantine as the Agents were resetting it. The can is the one object that survived their purge. When she cut her self, maybe she realized the truth, or had some form or power or aspect of the glitched area transferred to her.
Or maybe it was a ...
I think it's consequence. The whole story is this "haunted house" that allows the kids to do whatever they want, free to explore and roam. It's childhood. The agents' truck is the looming, oncoming reality of adulthood. They dispose of the magical playground, and the main character feels hurt, now outside of the consequence-free environment they came from.
What is the reason for Alexa's reaction?
There are a few reasons, including realisation her friends are dead, understanding their "experiment" with the runner has now worked and possibly terror given the attack she has just suffered at the hands of the machines.
Background to Matriculated:
In Matriculated, a group of human resistance ...
Ref - Matrix Explanation
Let’s take a step back into what really happened in the world in the
early 21st century. This information is from the series called The
Animatrix which takes a deep dive into what really happened. Do watch
The Second Renaissance Part 1 & 2. These short animated films were
released much after The Matrix. A synopsis from ...