I believe it must be a mechanism to hold the razor open in the shaving position but I agree with notitfortat that it would actually be obtrusive during use hence why we only see it on this one razor. Actually a Greaves with this mechanism showed up on Ebay last year and I saved some of the photos from the listing because it was so unique. This one must be an even earlier example as it is much more of the stubtail (actually no-tail) style and older looking, square-ish scales.
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