Do NOT stare into the Silverback gorilla's eyes. It is considered a threat & agitates them, if they meet your stare, look away. It's not a tip, it's just a recommendation to respect the animals.
It was a weird sad experience even for my 3yo. Watching lions standing in the mud against a grey sky makes you feel as guilty and stupid as a person can be. I so much regret I took part to this.