Ferae naturae

In Latin, “by its nature, wild”.

To be contrasted with animals mansuetae naturae, animals are, in the immortal words of Darling, J., in Manton v Brocklebank:

... those ferae naturae, e.g. tigers and lions which a man keeps at his peril.

A chap who keeps lions and tigers does so at his peril, and should they escape and cause damage to (for which, presumably, read “eat”) his neighbour the ordinary principles of Rylands v Fletcher will apply.

In fact as I recall the escaping water in Rylands v Fletcher was classified, in the eyes of the law, not as a wild animal, but as a domestic one with a known predisposition to flightiness.