Do the match in list context, and don't use $\d+ at all

if (@kitties = $string =~ /pattern (with) captures/) {
  paw_at @kitties;
}
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Obviously you can use my($cats, $kittens) in place of @kitties there.

The other option is check that the match succeeded first

if ($string =~ /pattern (with) captures/) {
  paw_at $1;
}
[download]

but $1 is ugly... unpacking into either an array or bundle of scalars will get you less maintenence-programmer hate.