Heard the former used for the first time, today. Quickly surmised (from context) it to be roughly equivalent to the latter. But, what is the actual physical motion involved (in the former)?
I.e., are the two thumbs pressed against each other? (palms facing, fingers steepled? or, twisted: one up, the other down?)
Or, is each thumb "held captive" by the other fingers of that same hand (e.g., like an ASL 't')?
Or, something else?