open( LOG, ">>", "log.txt" )
    or  die "Can't' write to log.txt: $!\n";
*STDOUT= *LOG;
print "Yay! This goes to log.txt! Success!\n";
# Reason 1:
system("echo Boo, this goes to the old STDOUT");
# Reason 2:
close STDOUT;
print LOG "Boo, this goes nowhere but I didn't close *LOG!\n";
# Reason 3:
open STDOUT, '>>', 'newlog.txt'
    or  die "Can't write to newlog.txt: $!\n";
system("echo Boo, this still goes to old STDOUT despite reopening");