If the cat was removed while purring, it never removed
the block against petting a cat at that spot, so if a cat was
later placed there without a server restart, it would not
be possible to make the cat purr again.
Instead purring automatically expires after 2 seconds if
not repeated by the DNT.
They currently aren't allowed to emit random
ambient meows, and they aren't able to run the
continued purring DNT, so to be consistent, just
disallow them from starting a purr too.
