The monitor is the screen a puppeteer watches while performing, showing the camera’s view rather than the puppet directly — and learning to trust it over your own eyes is the defining skill of puppetry for the lens.
Why it exists
A performer working below the frame lineThe frame line is the bottom edge of what the camera sees, a... has their arms raised over their head and physically cannot see the puppet’s face. Even when they can see it, what they see is not what the camera sees. The lens flattens depth, crops the frame and changes the eyeline entirely.
What it changes
Everything is judged on the screen. Is the puppet in frame? Is it looking at the lens or past it? Is the mouth reading, or is the head bouncing? A performance that feels right in the hand can be badly wrong on the monitor, and the monitor is the only opinion that counts.
The learning curve
The image is reversed relative to your movement, so moving the puppet right moves it left on screen until your brain rewires. Most performers describe this as the hardest early hurdle, and as something that becomes invisible once it clicks.
Placement
Low, close, and angled so it can be seen with the head tilted back and arms up. On a crowded set the monitor position is negotiated before anything is shot, because a performer who cannot see it cannot work.
In rehearsal
A phone propped up and recording will teach you most of this. You do not need a broadcast set to learn to work to a screen.
The hack: rehearse to playback before you rehearse to a live monitor. Watching yourself back builds the same instinct without the reversal problem fighting you at the same time.