This article is from the RCA SelectaVision VideoDisc FAQ, by email@example.com (Tom Howe) with numerous contributions by others.
Most of the skipping on CED's is caused by a condition RCA called "video
virus," rather than by actual damage to the disc grooves. If the
skipping goes away or becomes less pronounced when the same section is
played repeatedly, then the skipping is attributable to video virus.
This condition occurs when tiny dust particles on the disc surface have
become "glued" to the surface by the right combination of high
temperature and high humidity. Usually the stylus will break this dust
free the first time it hits the dust, but sometimes the contaminated
grooves will have to played a number of times to break the dust free.
Some discs will skip throughout play the first time they are played, but
then not skip at all on subsequent plays. This is because the disc has
not been played in a long time and required a conditioning play wherein
the stylus "cuts" a groove in the glassy smooth lubricant on the disc