This one example is explained in the tips and notes for the Sayings skill:
As happy as a shoe
Some Gaelic expressions can seem a little unusual at first glance. This next one is common and an absolute gem:
- Cho sona ri bròig. - As happy as a shoe.
Nobody knows what made the shoe so happy, and it certainly isn't telling anybody anytime soon.
Hawk-eyed learners among you may notice that the word bròg has been slenderised to bròig. We do not go into the grammar as to why this happens here (didn't want to rush it), but the change is caused by an aspect Gaelic's dative case.