Final answer:
Mr. and Mrs. Hadley screamed because they were startled and frightened by the sudden appearance and sounds of lions.
Step-by-step explanation:
In the last section, the two reasons that caused Mr. and Mrs. Hadley to scream were the sudden appearance of a wild animal, specifically lions, and the sound of the lions walking through the grass. The screams were a result of being startled and frightened by the presence and sounds of the lions.