Cockatrice
The cockatrice's eggs are the point at which a terrible danger first becomes apparent. While a cockatrice is a hideous mythical hybrid, figuratively the expression cockatrice's egg is used to refer to the point at which a terrible threat or danger first becomes apparent.
Proverbs 23:32 At the last it biteth like a serpent, and stingeth like an adder <06848>.
Isaiah 11:8 And the sucking child shall play on the hole of the asp, and the weaned child shall put his hand on the cockatrice <06848>’ den.
Isaiah 14:29 Rejoice not thou, whole Palestina, because the rod of him that smote thee is broken: for out of the serpent’s root shall come forth a cockatrice <06848>, and his fruit [shall be] a fiery flying serpent.
Isaiah 59:5 They hatch cockatrice <06848>’ eggs, and weave the spider’s web: he that eateth of their eggs dieth, and that which is crushed breaketh out into a viper.
Jeremiah 8:17 For, behold, I will send serpents, cockatrices <06848>, among you, which [will] not [be] charmed, and they shall bite you, saith the LORD.