Apparently, Levi can pull himself into a sitting position now. I only know because every time I go to get him up from his nap, instead of flailing around helplessly on his back, he's sitting up and peering at me through the bars on the crib.
This new skill of his has one major fault. Apparently the act of getting yourself from a supine to a sitting position is so exhausting, that once he gets there, he tends to nod right off.
Next lesson: lying back down before falling asleep.