Ajahn Karunadhammo reflects on the second foundation of mindfulness, mindfulness of feeling. In particular, Ajahn Karunadhammo speaks on Majjhima Nikāya 44, The Shorter Set of Questions and Answers, which discusses the three kinds of feeling : pleasant, painful and neutral. For a translation of this sutta see https://www.dhammatalks.org/suttas/MN/MN44.html