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.
(..) He would've grown up to be a rat. Stupid bastard! I can't believe you. Now you're going to dig the hole. I got no fucking lime. I will dig the hole. I don't give a fuck. Is it the first hole I dug? Not the first hole I dug. Where are the shovels? - Hello? - Hello! (..)1990 Goodfellas