$ perl -we '$a*=0'
Name "main::a" used only once: possible typo at -e line 1.
Use of uninitialized value in multiplication (*) at -e line 1.
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Only certain mutators suppress the warning - those that most make sense with a 0 / "" default. These are:

++ and -- (either pre or post), +=, -=, .=, |=, ^=, &&=, ||=.

But last I checked, some of those erroneously warn when used on a tied variable.