system
A chat on subreddit /r/me_irl
human
Gorillas are actually studied to be intrinsically peaceful animals that avoid violence at all cost unless it's a last resort. Theres plenty of footage of people on a foot tour going in to the wild and being amongst wild gorillas. Silverbacks make a whole big show at times with noise and jumping around but it's more often than not a bluff and so long as people exhibit signs of submission (head down, not looking straight in the eye etc) the silverback will leave them alone after that once the relationship is established. They will even permit humans to play with it's babies. 

You might want to read up on the effects of a Black Mambas venom on a human, you make it sound like taking a sleeping pill lol. I reckon you might change your mind.
gpt
We're talking about a mall. In the United States, the average shopping mall size  is 400,000 to 800,000 sq ft.  The odds of even encountering 1 black mamba per 100k to 200k sq ft in a 24 hr period is incredibly low (even if your job was to find one) as compared to trying to evade being noticed by a single gorilla.