Lip Sync   

With synchronous dialogue, the viewer can easily detect 2-3 frame discrepancies in lip to speech synchronization while an experienced editor can detect a single frame offset. 
A single frame in video is 33 milliseconds (ms) 
A single frame in film is 41 ms 
thus for film at 24 fps, 3 frames is 125 ms
or .125 seconds 
for video at 29.97 fps 3 frames is a 100 ms. 
or .100 seconds