This is the 3699th most frequent Russian word.
угрожать
To threaten.
The verb 'угрожать' is used here to describe the act of threatening, emphasizing the means (words) by which the action is performed.
Он угрожал мне словами.
He threatened me with words.
In this sentence, 'угрожать' is used metaphorically to describe a dog's behavior when barking in a defensive manner.
Собаки иногда угрожают своим лаем, чтобы отпугнуть чужаков.
Dogs sometimes threaten with their barking to deter strangers.
The adjective 'угрожающие', derived from 'угрожать', describes something (symptoms) that causes concern or alarm, extending the verb's meaning.