Once in a great while, when the positions of the stars are
just right, a seven-year-old rooster will lay an egg. Then,
along will come a snake, to coil around the egg, or a toad,
to squat upon the egg, keeping it warm and helping it to
hatch. When it hatches, out comes a creature called basilisk,
or cockatrice, the most deadly of all creatures. A single
glance from its yellow, piercing toad's eyes will kill both
man and beast. Its power of destruction is said to be so
great that sometimes simply to hear its hiss can prove fatal.
Its breath is so venomous that it causes all vegetation
to wither.

There is, however, one creature which can withstand the
basilisk's deadly gaze, and this is the weasel. No one knows
why this is so, but although the fierce weasel can slay the
basilisk, it will itself be killed in the struggle. Perhaps
the weasel knows the basilisk's fatal weakness: if it ever
sees its own reflection in a mirror it will perish instantly.
But even a dead basilisk is dangerous, for it is said that
merely touching its lifeless body can cause a person to
sicken and die.
[ Mythical Beasts by Deirdre Headon (The Leprechaun Library)
and other sources ]