(On an agreement being implied & unforeseeable events)
James Scott and Sons Ltd v. Del Sel  SC 592 per Lord Sands at 597: “A tiger has escaped from a travelling menagerie. The milkgirl fails to deliver the milk. Possibly the milkman may be exonerated from any breach of contract; but, even so, it would seem hardly reasonable to base that exoneration on the ground that “tiger days excepted” must be held as if written into the milk contract.”
Tiger days. Awesome.