Clasp-knife

...there is yet ample evidence of the existence of clasp-knives ages before the production of the Canterbury Tales. Among Etruscan antiquities in the Bronze Room of the British Museum are several clasp-knives, some of them with bone, others with bronze hafts, their blades being of iron — a metal employed for cutting implements by the Tyrrhenian tribes, at a far remote era. A scalprum or penknife has been found in Rome, the blade shutting into a bone haft, which is carved to represent the upper half of a human body; and clasp-knives, with iconic handles of the Roman era, have been discovered both in France and this country.

Source: wiktionary

“Well, this knife is called a clasp-knife, because it shuts and opens, as you see, and it has three blades — a big one for cuttin’ up your victuals with, as you see me doin’; and two little ones for parin’ your nails and pickin’ your teeth, an’ mendin’ pens an’ pencils — though of course you don’t know what that means.”

Source: wiktionary

Blake picked his teeth reflectively with the point of a clasp knife.

Source: wiktionary