Java: Word calculator

I've made a word calculator in java, it works like this:
you enter: fourteen thousand two hundred and six multiplied by twenty seven thousand eight hundred and nine.
answer: 395,054,654.
It works for input numbers up to 999,999.

I would like to know what you think what input would screw it up.
It doesn't do more than one calculation at a time.
It works for entering in numbers in decimal form.

I would like to know what you think what input would screw it up.
How does it handle negative numbers; the input "negative zero;"
excessive use of "and" or lack of "and;" disorganized numbers - "ten hundred and seven," "ninety thousand ninety-nine hundred nine nine;" fractions as numbers (when fractions are not supported)?
What kind of precision does it handle and what kind can it handle up to?
How do misspelled words, actual numeric input, and characters the parser does not recognize affect the processing?
Divide by zero?