Perl isn't a statically (or even strongly) typed language. It generally tries to do "something sensible" (or "Do What I Mean" - abbreviated as DWIM) with data.

If you're trying to use a string as a number, it will do a string->numeric conversion (handling leading spaces and stopping at the first non-digit).

This behaviour is generally useful and time-saving. One places where you may get caught out by it is in boolean true/false tests. All the following are false (nothing is printed):

print "a" if 0;
print "b" if "";
print "c" if "0";
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the one which surprises people the most is "c" not being printed.

Dynamic languages can require a bit of mental adjustment, C, C#, C++ and java programmers are used to having the compiler catch certain classes of errors. Perl will only catch similar errors at runtime (and will work around others as we've just seen).

For those that like dynamic languages, the general view is that you are more productive in them (since type declarations littering your code make it more brittle - i.e. harder to change and adapt it) and that computer-checked correctness is better achieved via unit testing, to verify the dynamic behaviour.

There is a well-established culture of unit testing in perl, with good modules to support it's use and most (all?) CPAN modules including a test suite.

Lastly, I think perl6 will bring such (optional) type annotations to the language, but I'm not sure and don't know the details.