The Wild Beast Theory

The person who for his own purposes brings on his land and collects and keeps there anything likely to do mischief if it escapes must keep it at his peril, and if he does not do so, is prima facie answerable for all the damage which is the natural consequence if it escapes (Rylands vs. Fletcher).

In this case, it is not necessary for the plaintiff to prove negligence on the part of the defendant.

The defendant cannot raise the defense that he has taken all possible precautions to prevent damage or injury.