$ perldoc -f sqrt

  sqrt EXPR
  sqrt    Return the square root of EXPR.  If EXPR is
          omitted, returns square root of "$_".  Only works
          on non-negative operands, unless you've loaded the
          standard Math::Complex module.

          use Math::Complex;
          print sqrt(-2);    # prints 1.4142135623731i

UPDATE:
But i didn't really answer the question, "why can't you 'catch' this exception" ... is it possible? Why yes it is! Fletch++!

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)