Contra Dance Handshakes

In contra dance you'll sometimes hear people talking about a handshake grip. Perhaps the caller says "shake hands with your neighbor, and pull on by" or "take right hands, you balance and box the gnat". Thing is, it's not a standard handshake:

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Full Handshake

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Finger Handshake

This phrasing misleads new dancers without giving much help to experienced ones. In my calling I've switched to saying "take hands" where I would have said "shake hands".

But now I'm curious: is there anywhere that people shake hands like this, with their fingers? Did people used to do full handshakes in contra? Finger handshakes outside of contra? Where did this come from?

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