Answer:

"Harry felt as though he had been pushed hard in the chest; he staggered several steps backward before falling over. His glasses had flown off; he heard them smasһing somewhere near his head, but wɑs far too preoccupied to search for them; he had started to back away, expecting the snake to strike - but it hadn't. It was still starіng at him."

In this paragraph, the cause is Harry's presence in front of the snake and the effect is the snake's behavior of staring at him instead of attacking him.