sub interlace {  # 52
my$x=pop;my$y=reverse+pop;$x=~s/./chop($y).$&/esg;$x   
}

sub interlace {  # 47
my$x=pop;@_=split//,pop;$x=~s/./shift.$&/esg;$x   
}

sub interlace {  # 45
($_,@_)=(pop,split//,pop);s/./shift.$&/esg;$_  
}
[download]

Update: here's a shorter one, without said warning.

sub interlace {  # 43
$_=shift;@_=split//,pop;s/./$&.shift/esg;$_   
}
[download]