Recent DD wotds have been less than inspiring because the words themselves have no interesting evolution from their etymology.
Jocular derives from a diminutive of "iocus" for joke (remember, there is no "j" in Latin), and gives a straight line to the usage "characterized by joking". A fitting word for April Fools Day, but there was no jocularity today. Just business as usual--singing, more singing, and judging moot court. Oral argument before the Supreme Court is no place to be jocular. While courts appreciate humor and the occasional wit, jocularity is frowned upon as too casual. His jocular attitude in class of making wisecracks often had him sent to the principal's office. And it only applies to people since people are really the only ones who can make a joke. The chimpanzee could only mimic a jocular demeanor, which was in fact, really only juvenile. A robot can only be programmed to respond in a jocular manner. But it is inherent in the word that jocular has creativity, so other mammals and certainly tangibles and abstracts are not jocular. A jocular wind would actually be "playful" at best. A jocular essay might work, but as discussed in past words, only because the thing is so closely associated with the actions of people. As opposed to a jocular bookcase, which might only exist in Lewis Carroll's imagination as warped and barely functional for it's intended purpose, although I'd say this would better describe whimsical or perhaps, dysfunctional or pointless.
Undulant on the other hand comes from the Latin diminutive "undula" for wave, again straight to resembling waves in form, motion or occurrence. So, we can discuss the height, depth and period of a wave. Ironically, undulating waves is practically redundant, but unfortunately, all too commonly used. The hills created an undulant landscape. The equation represented a simple undulating sine curve. A bit pedantic and geeky/poetic, but accurate. Her head undulated while she sang, demonstrating her poor technique and lack of self control. His undulant voice lulled the baby to sleep. Possibly. Her country twang had a pronounced undulant quality. His undulant moods betrayed his bipolar disorder? Yes. Even after several years, she was still struck with undulant bouts of inconsolable grief mourning the death of her father. Yes, absolutely, and quite evocative, although I might take it a step further with drowning bouts or floods or for the really bad one, tsunamis. So, yes, it works for people, their activities, tangibles and abstractions. Enjoy!