Consider this real situation: Light from a far-background galaxy is observed to be lensed by a closer massive galaxy. Individual photons that graze the closer galaxy travel to the observer along various geodesic paths, as prescibed by GR. Now consider a very hypothetical situation. Suppose a point on the background galaxy is connected to the observer by a weightless stretched string. Does this string lie along a geodesic? Or, more simply: in principle, do laser pointers and builder's chalk lines define "straight lines" equally well? If so, why should they?