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.
(..) this is your lucky day. We got Condition Red and we're definitely eXpecting rain. Outstanding, sir. We taking care of business?. Well, the NVA are dug in deep. Hotel Company's still working this side of the river... ...street by street and house by house. Charles definitely got his shit together... (..)1987 Full Metal Jacket