logical deduction - Infinite precision

The man tells you, "To enter the door of infinite precision, you must complete all of these tasks perfectly:

• Hold in front of me a baby that is exactly two days old.


• Bring me a metal object that weighs exactly one kilogram.*


• Bring me a stone object that weighs exactly one pound.*


• Bring me a glass containing something other than water that is exactly the same density as water.



• Write all the digits of pi."

"I'm sorry", you say, "but that is impossible. I can complete four, but there is one I cannot do."

Which task can't you accomplish, and why?

(The explanation should state how you can do the other four tasks, as well).

Hint:

Keep in mind that this puzzle was spoken, not written down. This may help with one of the tasks.

*If you want to get technical (and I know some of you do), consider these objects with a mass of one kilogram and one pound.