German/Swiss/Austrian superstitions

[pastimperfect]

DC has to write an essay about superstitions in German-speaking countries. We've been able to find out about some, but we're struggling to find the reasons behind the superstitions and whether they are still observed.

So now I'm wondering if the collective power of Mumsnet can help us? Or at least point us in the direction of websites that can do more than tell us it's bad luck to walk between two old ladies, but what we might be risking.

I've put this in "chat", too, but then thought it might be better in here.

The two I know which don't exist in Anglophone countries, and which are taken very seriously here, are that people should look each other in the eye when saying 'cheers' with a round of drinks (apparently the consequence of not doing so is 7 years bad sex), and not celebrating a birthday ahead of time. So if your birthday is on Tuesday, for example, you would celebrate the weekend after, but never before. The one acceptable exception is celebrating the evening before and keeping the party going to and beyond midnight - a practice so common it has its own verb: reinfeiern means seeing in your birthday with a celebration.
The other superstitions I know here in Germany are similar to English ones - not walking under ladders, black cats, spilling salt etc.

Ooh, a few more have just occurred to me:

Germans press their thumbs rather than crossing their fingers in order to hope that something will go well. The expression is 'Daumen drücken'. Apparently it's because the thumb was seen as the strongest and most important digit.

Breaking a mirror is 7 years bad luck, like in the UK - but there's a weird tradition with pottery. The night before a wedding there will be a party with both bride AND groom called a Polterabend, and lots of pottery will be deliberately smashed by their friends to bring good luck. Polter is the same root as Poltergeist! I think other cultures have the same superstition - Greece perhaps?