Technically speaking, in Poe's story "The Black Cat" the first thing that 'happens' is that the narrator informs us he is going to die tomorrow and wishes to unburden his soul tonight by exposing "a series of household events" that have terrified, tortured, and destroyed him in the time leading to this moment.
You asked which events happen first, but I am not sure how far into the narrative you would like to consider as "first events". The sequence of events he describes are as follows:
1. The narrator had a normal childhood and was known to be docile and fond of animals.
2. As a young man, he married a woman who also loved animals and brought a lot of pets into their household.
3. The narrator developed a fond relationship with their black cat named Pluto.
4. The narrator began to drink excessively, which resulted in violent tendencies.
5. One day while drunk, the narrator cut out Pluto's eye with a penknife.
6. Pluto thereafter began to avoid the narrator, which caused the narrator to...
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