from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
WELL KNOWING. These words are used in a declaration when the plaintiff sues
for an injury which is not immediate and with force, and the act or
nonfeasance complained of was not prima facie actionable, not only the
injury, but the circumstances under which it was committed, ought to be
stated, as where the injury was done by an animal. In such case, the
plaintiff after stating the injury, continues, the defendant well knowing
the mischievous propensity of his dog, permitted him to go at large. Vide
Scienter.