As has been hinted, Holland could be rather a fidgeter. Notes from meetings might have swirls in the margins, any piece of paper near the phone could get squiggled on during a long conversation, and if you happened to be in the wrong place when the mood was on him, you got drawn.
My brother was happily reading a book when this happened:
[James, pen sketch undated, in a private collection]
A dog we looked after a couple of summers in the south of France was resting after a long walk:
[Mopsic, pen sketch, 1975, in a private collection]
My mother was relaxing and watching the television:
[Watching television, pen and monochrome water colour, undated, in a private collection]
As the author of this website, I can at least draw a veil over those times I too got caught!