Echoing the plaint of many a desperate bathroom-seeker, Willis offers an extended series of rhymed speculations about what’s holding up the line for the loo. This is bathroom humor in its purest form: “Is it a tiger who needed to tiddle? / A wandering wombat who wanted to widdle? / A waddling penguin too frozen to piddle?” Rising ingeniously to the challenge, Reynolds depicts a menagerie of easily recognizable animals, discreetly but unmistakably engaged in elimination or other restroom activities as a long queue of humans waits outside with varying degrees of patience. For bladder or worse, rare is the child who won’t “go” for this, despite its unexpectedly low-pressure dénouement. (Picture book. 5-8)