WoWInterface - Chat Event Pet Feeder Script help

This script works fine if you type in the pet name manually, as it appears in the Chat Frame (substituting UnitName('Pet') for the actual name):

Code:

function PetActionEXPBar_FeedPet()

        local petname = UnitName("Pet");

        if ( event == "CHAT_MSG_SPELL_PERIODIC_SELF_BUFFS") then

                if arg1 == ( "UnitName('Pet') gains 1 Happiness from Feed Pet Effect." ) then

                PetEXPBarFeedText:Show();

                PetEXPBarFeedText:SetText("1 Loyalty Gain");

                end

        end

end

Is there any way to insert the local 'petname' variable into the Arg 1 conditional and have it match the chat frame text?