SuperDave,
I'm assuming it was old, fresh from the paint tote? I've tried breaking medium thickness paintbrushes with my bare hands and its difficult since they taper from one end to the other, so are more likely to snap at the thin end.
The very thin paintbrushes can be snapped in two manually but as they become thicker it becomes more taxing, particularly on the fingers.
Most likely successful snapping will be relative to the strength of the person applying the force, so for Mr Universe its no problem, etc.
I've no real preference for how the paintbrush was broken, just that pragmatically placing it against the wall and stepping on it seems the cleanest and quickest way to deliver a paintbrush in two parts?
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