The herd of lions heard a sound that was similar to the cry of the enemy which caused them to put up their guard and start walking around.
この場合、次のような言い方ができますよ。
ーThe herd of lions heard a sound that was similar to the cry of the enemy which caused them to put up their guard and start walking around.
「ライオンの群れは敵の鳴き声に似た音を聞いたので警戒し見回り始めた」
herd of lions「ライオンの群れ」
cry of the enemy「敵の鳴き声」
to put up one's guard「警戒する」
to start walking around「歩き回り始める」
ご参考まで！
It started to look around carefully to make sure there were no enemies.
ご質問ありがとうございます。
・「It started to look around carefully to make sure there were no enemies.」
（意味) 警戒して敵がいないか見回りをし始めた
<例文>It started to look around carefully to make sure there were no enemies at night.
<訳>夜に警戒して敵がいないか見回りをし始めた。
参考になれば幸いです。
カナダ 
アメリカ合衆国 
