I find it amazing the number of birds and bugs that make noises along the side of the road that sound exactly like squeaky, poorly lubricated drive chain components.
I also find it amazing how they are organized and will tail you for hundreds or yards (or pass off the noisemaking duties to their brethren) so that you are almost convinced "I'll have to look into that when I get home" and then once you leave their habitat, all returns to silence!