Sorry to backtrack a bit to earlier discussion here... and some may wish to scroll by if they found MassGuy's string and ruler experiment to be distasteful. (I found inspiration in the experiment, myself.)
I visited with my 7 & 9 year-old nieces this afternoon. We did some crafts, including pretty, decorated cardboard 'frames' to show off their lovely artwork. I cut an 8" hole in each of their cardboard rectangles, and before we decorated, casually asked them if they thought they could fit their whole bodies through the hole. They thought it was a hilariously fun game, btw. The youngest (who's almost 8, actually, but rather small for her age) fit through quite easily, save for a bit of wriggling when she passed her shoulders through (arms stretched up above her head). I don't even think she'd have had to wriggle if she hadn't been wearing a somewhat bulky sweater, tbh. Her big sister was a little disappointed that hers didn't quite fit, so we cut an extra inch out of the centre, and she, too, was able to pass through the bigger circle ~ much to her delight.
I found it oddly reassuring to think that those sweet little angels perhaps didn't undergo the kind of extreme manipulation that I'd thought may be required to fit through those tiny tank openings. I realize that a flat cardboard cutout isn't going to offer the same kind of rigid resistance that the metal tanks would, but still made me optimistic that at least they may not have endured that additional torture.