Why do cats purr?

I know that cats purr for a variety reason. They purr while content, when anxious, while giving birth, and even just before death. I’m also familiar with the healing properties of purr frequencies.

We just adopted a few cats and one of them purrs at nearly every opportunity. I suspect this is an expression of the anxiety of exploring a new home and adapting to new owners.

Out of curiosity though, does your cat purr for seemingly random reasons? What strange situations have elicited purrs from your feline?