A knife has a housing, a blade having a cutting edge and mounted on the housing with the edge extending transversely of a predetermined direction. An actuator is movable on the housing and pivots a blade guard on the housing about a guard axis for movement in the predetermined direction from a safety position in which the blade guard covers the cutting edge of the blade into a cutting position in which the blade guard is spaced from the cutting edge and the cutting edge is freely accessible and from the cutting position in a direction opposite the predetermined position into the safety position.