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.
(..) to take us on a tour... of the East River. Did he say what was buried in the flower bed? Yeah. He said the dog got too inquisitive, so he dug it up. It's in a hat box over in his apartment. Want to look? No, thanks. I don't want any part of her. (..)1954 Rear Window