Front Porch Rocking

An elderly couple was rocking on their front porch one afternoon when ma all of a sudden doubles up her fist and cold cocks pa knocking him off the porch. He gets up and dusts himself off and returns to his rocker. After rocking for a while he turns to ma and says what was that for ma? And she says for having a little one. A little while later pa doubles up his fist and cold cocks ma knocking her off the porch. She gets up dusts herself off and returns to her rocking chair. After rocking for a while she says to pa. What was that for pa? He says for knowing the difference.