How Much is that Birdie in the Window

Itzik Smadar went into a pet store in Jerusalem, wanting to buy a parrot. The shop owner pointed out three identical parrots on a perch and said, "The parrot to the left costs 1000 shekels."

"Why does that parrot cost so much?" Itzik wondered.

The owner replied, "Well, it knows how to use a computer."

Itzik asked about the next parrot on the perch.

"That one costs 2000 shekels because it can do everything the other parrot can do, plus it knows how to use the UNIX operating system."

Naturally, Itzik asked about the third parrot.

"That one costs 5000 shekels.”

"And what does that one do?" Itzik asked.

The owner replied, "To be honest, I've never seen him do a thing, but the other two call him Rebbe!"