You just drop one surreptitiously and it’ll run off and make a nice loud noise out of sight, giving you a diversion if you need one.
"Right," said Harry, who had more pressing matters on his mind than Snapes detention, and now looked around surreptitiously for some indication of what Dumbledore was planning to do with him this evening.
Harry glanced around surreptitiously.
Instead, he surreptitiously folded down the corner of the page.
It was, however, eclipsed almost immediately by a glow of smugness at the thought that, deficient though he himself might be in the area of materializing out of fireplaces, there had never been a murder in any of the government departments under his charge… Not yet, anyway… While the Prime Minister surreptitiously touched the wood of his desk, Fudge continued, "But Blacks by-the-by now.
There are no more uses of "surreptitious" in the book.