As Newt, Jacob, Tina, and Nagini entered the center of the lost city, they saw it was a dark room in which there wasn't much light. It appeared to be a tomb.
"It appears to be a tomb," Newt said for the benefit of anyone in the audience who hadn't already figured out that it appeared to be a tomb. "But for who?"
"You mean, 'for what,'" said Tina, ducking to get through the door with her antlers. "Look at the size of that sarcophagus. This wasn't for a human."
"Oh, so only humans are considered 'whos?'" Newt replied heroically. "Every other creature on this planet is a 'what?' You know, that attitude is just one step short of considering Muggles to be 'whats.'"
"What?" asked Jacob.
"Forget it," said Tina, and then she turned to open the sarcophagus. She tried Alohomora, Bombarda, and, for some reason, Expecto Patronum. None of them worked, especially not Expecto Patronum.
"Pickett, see if you can get that open," said Newt, keeping his fantastic beasts relevant to the story.
Pickett leapt out of Newt's pocket and onto the sarcophagus. He then climbed inside of it and did something to make it open up. By the way, it turns out that Pickett later becomes Cedric Diggory. This is canon now.