I wonder where the switch is?
Pulaski holds it between her thumb and first two fingers at approximately the midpoint of the body, but in the later episode it's held closer to the small end. If it's a momentary switch, it would have to be somewhere in the middle of the long face, approximately where Pulaski's thumb is -- it's the only overlap in finger position between the two appearances:
Or it could be a slide switch in which case the finger position wouldn't matter. Watching the scene from "The Child" at one point there seems to be something in the recess on the small end of the marker body - could be a slide switch?