乘虛而入 的英文怎麼說?

[1] take advantage of somebody when they are weak or in a disadvantageous situation[2] catch somebody by surprise[3] catch somebody off guard

英文中沒有此成語的說法，所以只能按情況白話翻譯。Catch somebody by surprise 跟 Catch somebody off guard 意思是當某人沒注意到的時候做了某件事情