Focus breathing

Pull focus from a near subject to a far one and on many lenses the framing changes a little at the same time. Nothing has moved and the focal length has not changed, yet the angle of view has shifted, so the image looks like it breathed in or out. Cine lenses are built to suppress it, which is part of why they cost what they cost. Stills lenses vary wildly, and some recent cameras correct for it in software. On a locked-off talking head it is invisible. It becomes obvious the second you rack between two subjects on camera, so test the lens before planning a shot around a focus pull.