The night after Nana and Pop Pop returned from their California trip, Arthur showed off to Pop Pop by learning how to move from a crawling position to a sitting position, and back again. It was a very slow process, but he was deliberate and careful with his movements so that he wouldn't topple over. And then this morning, when Arthur woke up crying at 5am, when I went over to check on him, he was sitting upright in his crib. Evidently he mastered this skill in short time, and we are quite glad we lowered his crib mattress the other day. Now it seems he is considering pulling himself upwards on the living room furniture. No progress yet, but it is definately on his mind.