Can we make isoglosses?

[Koen G]

So still no idea what a "gaismich" could be.  gais- is probably goat but I cannot think about anything for -mich, it's not a suffix that makes sense. A tithe or rental fee related to goatkeeping? Four geese was a substantial payment for a tax.

This is an interesting line of reasoning, to think of the animals as "animal to be paid for...". It could be for a certain day, but also for a certain service. Maybe the geese are a tax on the right to sell goat's milk?