This is one of my favourite on screen mistakes in SG1. From season two, The Serpent’s Lair. Richard Dean Anderson was off camera reading the script, and as the camera pans round, he panics and tries to throw the script off camera, utimately failing. If you listen carefully you can even hear the script rustle as it’s thrown.
The script is visible on the right hand side of the screen, behind Bra’tac. The best part is watching Amanda Tapping glaring at Richard and Michael shanks just looking like nothing has happened.