If a smoothly varying, range-independent sound-speed profile and its first derivative are known everywhere, in principle it is possible to trace classical rays through it with arbitrary accuracy. In practice, sound-speed profiles are often delivered to modelers as a set of discrete speed/depth pairs, and only the values at sampled depths are known a priori. Some form of interpolation must be used to estimate the profile at depths between the sampled points, and cubic splines were proposed nearly 30 years ago as a convenient (though not the only) and computationally simple way of doing this. However, when spline fitting is used, errors in the ray paths arise due to the splining errors. Using a simple (Munk) sound-speed profile, the magnitude, behavior, and causes of such ray-path errors are investigated.