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.
(..) Something pretty big was gonna happen here. Good work, Mac. Clear the area. No traces. Get the men ready to move. Son of a bitch is dug in like an Alabama tick. - You're hit. You're bleedin', man. - I ain't got time to bleed. You got time to duck? This is goddamn beautiful. Goddamn jackpot. (..)1987 Predator