Logic Masters Deutschland e.V.

I need to start off by crediting a number of people, without any of whom this puzzle wouldn't exist. It was initially inspired by SlowLarry & Philip Newman's collaboration, Why Can't We Be Friends?, which I must confess I watched Simon solve on Cracking The Cryptic rather than tackling myself. In the comments below that video, YouTube users Parlyne & WhistleHummer discussed some of the fun and interesting properties of friendly cells, particularly in relation to drawing paths of them through the grid, and it was these observations that led me to ask myself if it was possible to... well, spoilers! I should also thank Lemony Snicket for embedding within my subconscious the perfect name for the puzzle, or at the very least the one that's the most fun.

You may now skip to the rules if you'd like, but otherwise I'd like to issue two caveats. Firstly, in what is almost becoming a pattern with my puzzles, one of the corners is perhaps a touch thornier that I would have liked. It is more achievable than it was before I added the ratio dots, but it does still require a bit of poking around, even if you can do it fairly smoothly if you've been keeping on top of your deductions. That said, if you've got a hankering for some heavy bifurcation and a couple of hours to kill, you can always have a go at determining ~95% of the snake with no other information whatsoever. It can be done. I had to do it, in order to set the puzzle. I'm still not sure if I regret it. Secondly, I've been proven to be a terrible judge of difficulty, but I would say that, if you have previous experience of friendly cells and/or take a few minutes to play with them and see how the behave, then you will definitely find this puzzle easier than if you were to just jump in and figure things out on the fly. Would it then be four stars of difficulty? You tell me...

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Rules
Normal sudoku rules apply.
A cell is considered to be "friendly" if its value matches at least one of its row, column or box numbers, as counted in the standard way. For instance, the top right cell would be friendly if it had value 1 (for its row), 9 (for its column) or 3 (for its box), and the middle cell can only be friendly if it contains a 5.
The Incredibly Deadly Viper, being "one of the least dangerous and most friendly creatures in the animal kingdom", forms an orthogonally-connected one-cell wide path that visits every cell that is friendly in the completed grid and no others. It slithers between the two cells marked with white circles (which must therefore be friendly themselves) without ever touching itself orthogonally - diagonally is fine.
Digits in cells separated by black dots must have a ratio of 1:2. Not all such dots are given, and The Incredibly Deadly Viper is free to slither next to and through them if required.

You can tackle this on f-puzzles here, where there's also a rather more concise (read: flavourless) summary of the rules. I'm all ears for feedback, especially if you discover that the slippery little blighter's got another possible path through the grid... I'm like 99.9% sure there's only one route it can take, which near-inevitably means it's got loads. Still, I hope you enjoy the puzzle, and good luck!