This extract is taken from the novel Night Crossing by Samuel Obi.

Night Crossing (extract)

The border post came into view at half past two in the morning, and Yusuf felt the others shift behind him in the truck, a collective tightening he could feel through the boards.

He had crossed borders before. He knew the different qualities of waiting: the waiting that was merely administrative and the waiting that was not. This was the second kind. 5

The truck stopped. Outside, a generator hummed. Lights moved.

"Don't speak unless spoken to," said the man in front, not turning his head. His name was Fares and Yusuf had paid him four hundred euros and trusted him to the degree that the situation allowed. 10

"I know," Yusuf said.

Fares turned then. In the low light his face was difficult to read. "I mean it."

"I know," Yusuf said again.

Footsteps on gravel. Then a pause that seemed to last longer than physics permitted. 15 Yusuf counted his breath: one, two. Someone coughed at the back of the truck. He thought: don't cough again.

The footsteps moved on.

For a long moment no one spoke. Then Fares exhaled slowly, the specific sound of someone releasing the version of the future that had not happened. 20

The truck began to move.

Yusuf's hands were still clenched around something. He looked down. He had been holding his son's drawing: a house, a tree, a figure with its arms out.

How and to what effect does the writer build tension in this text?