A pre-lap is when the dialogue (or any sound) from the next scene starts before we cut away from the previous scene. They are a common and useful transition.
Pre-laps are often inserted in editing, but they can also be written into scripts.
Dialogue pre-laps are indicated with the parenthetical “(PRE-LAP)” next to the character’s name — not below it — and in all caps:
EVAN (PRE-LAP)
Oh man, that looks good.
INT. A LOTTA GELATO – DAY
Evan watches as Adam eats.
EVAN (CONT’D)
Stupid fluoride.
If the sound is something other than dialogue, it can be set off like this:
ADAM
How bad can it be?
PRE-LAP: A drill BUZZES.
INT. THE OFFICE OF DR. BOLSKI, DDS – DAY
Adam watches as Evan writhes in pain under the dentist’s tool.