Despite their last couple albums’ self-conscious departure from stunt-stuffed, goofy tunes in favor of more mature, somber material, the best song on Barenaked Ladies’ sixth CD is about bathing, joyriding, and lingerie-wearing monkeys (“Another Postcard”). Not that the Canadian quintet doesn’t ably maneuver through a dozen or so songs about love, life, death and other deep subjects; it’s just that the silly one about fun-loving, mailbox-bound chimps sticks with you much longer.