Gag and Sight gag

Gag noun - Something said or done to cause laughter.

Sight gag and gag are semantically related. In some cases you can replace phrase "Sight gag" with "Gag", this terms are similar.

Sight gag noun - A joke whose effect is achieved by visual means rather than by speech (as in a movie).

Gag and sight gag are semantically related. You can use "Gag" instead a noun phrase "Sight gag".