This has been dealt with on, I think "Films of the 50s," but it's all guesswork. The ol' lady is on some sort of wheeled device presumably pulled or pushed by offscreen grips (or tugged by "invisible" wires.) I suspect the rope gag is similarly an on-set wire gag where some piano wire is actually doing the pulling, with the noose rope following it around the woman's legs (possibly some other woman; it's an insert shot as I remember and doesn;t show her face.) The uncoiling effect is the same shot printed backward. In the interest of confusion, I'd guess that maybe that's backward-- that the "forward" shot is actually the "uncoiling" version of it, and the boa-like motion of the rope enveloping her legs is actually the version printed backward.