He was in Then a niggling doubt pricked at his brain.

But it didn't take away the niggling doubt in the back of his mind.

Probably nothing, he murmured, but there was a tiny niggling doubt in the back of his mind.

The last niggling doubt he had about carrying out the ceremony evaporated.

Although at the back of Hannah's mind there was a niggling doubt, given the situation.

Blake awoke the morning of the third day with niggling doubts.

The only niggling doubt in her mind regarded the love potion.

The niggling doubt lay in his gut like a stone.

Of course, this is usually so, but I am having little niggling doubts about such a sweeping statement.

But casting niggling doubt on various witnesses was one thing.