At least three possibile execution ways are known.
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* SPOILERS *
All involve hidden compartments and depth deception.
The cases are usually deeper or larger; assistants can usually crouch or weave, and saws never actually touch them.
Two methods employ fake feet of some kind; they can be recognised because fake feet, especially in older tricks, lack mobility or natural shape.
When they move, they do in a predictable manner.
The third, more cumbersome, method, usually requires a larger or oddly shaped cabinet. Train sawing tricks usually fall into this category.
Two assistants are needed too; one will take the upper part of the case.
She is the visible assistant.
The other one will usually stay crouched under a hidden compartment, and when needed, she will stretch her legs out of the holes.
If you watch closely, you can notice the legs in this vid do not extend naturally from above, but especially in the end, the camera pans too closely, and you can see the legs flexing back down.
This variation is usually the best for staged tickling, because you can actually have audience touch the feet, to show they are real.
On the downside, it is more expensive as a trick: you need a larger box, and you have to pay two assistants as opposed to one.
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Related to this third "Goldin" type sawing trick, are the "saw in thirds" and "belly sawing", both involving belly removal or piercing: the platform is usually hollowed out, and assistants lean deeper, under the cut line.
This kind of tricks requires but one assistant, and since she's just flexing her back, he legs and feet are her own, so - again - stage tickling is possible, both as a distraction to the audience and as comedy.
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If you are interested, you could check wikipedia for more.
