Tainting works per statement: if any tainted values are seen during execution of that statement, the rest of the statement is marked as tainted for the purposes of refusing to execute tainted code. kill is one such built-in that dies if it detects taintedness:

$ perl -T -e 'kill $ARGV[0]' 0
Insecure dependency in kill while running with -T switch at -e line 1.
$ perl -T -e '$ARGV[0], kill 0' 0
Insecure dependency in kill while running with -T switch at -e line 1.
$ perl -T -e '$ARGV[0]; kill 0' 0
$
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Dave.