The detectives 'dug into' his past and learned that he had once lived in another country.
Her fingernails 'dug into' my hand. = She 'dug' her fingernails 'into' my hand.
The salesman 'dug in his heels' and refused to lower the price any further.
(..) One of them could have been following him, but... we've got nothing to go on. Oh, I wouldn't say that. OK. Give me. The bullet they just dug out of the wall's from a handgun. A kill shot over that distance, from that kind of a weapon, that's a crack shot. But not just a marksman, a fighter. (..)2010 TvShow: Sherlock Title: A Study in Pink Season: 1 Episode 1