Sentence:  And listening to such a conversation one morning while taking a cup of chocolate in a cafe , Rousseau found himself bathed in perspiration , trembling lest his authorship become known , and at the same time dreaming of the <WSD>startling</WSD> effect he would make if he should proclaim himself suddenly as the composer . 
Meaning of the word marked with <WSD> tags:  so remarkably different or sudden as to cause momentary shock or alarm