It's archaic biblical language - don't worry about it. This usage of shall doesn't really exist in modern English.

As cultural background, you might want to know that a) it's a joke, and b) it refers to a famous passage in the Bible. The passage is "Isaiah 11:6," verse 6, chapter 11 of the Book of Isaiah. The original is written in Hebrew. King James of England commission an official English translation, issued in 1611, known as the "King James Version." For centuries, English speakers regarded this as "THE Bible." Even today, when people quote the Bible, they often quote from this 1611 translation, which used antiquated English. In the King James version, the verse is: "The wolf also shall dwell with the lamb, and the leopard shall lie down with the kid; and the calf and the young lion and the fatling together; and a little child shall lead them." Shall, shall, shall. In a popular modern translation (NIV), the same verse is translated: "The wolf will live with the lamb, the leopard will lie down with the goat, the calf and the lion and the yearling together; and a little child will lead them." Will, will, will. It is a prophecy of a time of peace when animals that normally would kill each other will live peacefully with each other. The joke says that MAYBE they are going to lie down together, and MAYBE the lion won't kill the calf--but "the calf won't get much sleep." That is, the calf is still not going to trust the lion. I am fond of a famous painting by the American "primitive" artist, Edward Hicks. The painting is called "The Peaceable Kingdom" and it depicts this scene. You can see it here: http://tinyurl.com/pc558ul The animals and children are in the foreground. There is an interesting detail in the background. The men in hats are in traditional Quaker costume. The men at the left are Native Americans ("Indians.") This is a historical event: William Penn's treaty with the Indians.

For the purists: 1) Will should be replaced by shall for the 1st person ( I and we) to form the future tense 2) Will can also be changed to shall for the 2nd and 3d person when there is a strong determination/ obligation e.g.: "You SHALL certainly do that!" or "There is no doubt: this SHALL happen!" (It is still used occasionally in the UK)

'Shall' = 'will'. In contemporary American English, the auxiliary verb shall is rarely used. In British English, shall and will are often used interchangeably with no difference of meaning in most circumstances. Internationally, will is now the standard choice for expressing future plans and expectations.

Georg is correct. In American English "shall" can also mean "must", but it is usually only used that way in legal documents.