There are many old snake-type soft plastics, most discontinued.
The first one that comes to mind has the same action as a water snake slithering across the surface: Bill Norman Snatrix.

An exact copy was sold by Ditto (shown) but revised due to design infringement and called the Gator Tail. The tail was thicker and had serrations on its outer edge.
Culprit still sells a Ribbon Tail worm that's similar in tail action to the Snatrix.

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Well, there are kits out there to make rubber worms, right? So you can make the body of the "snake"
I have made copies of worms in plaster that came out very close to the original, afraid the design would be discontinued or the company going out of business as in the case of Bill Norman.

Amazon has many mold designs going for as little as $10 for single cavity molds. Ebay sells a snake-cavity mold for $18.
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