Your child has another fever. Just when you were recovering from your fear of contamination from the bird feather collection stored in her drawers and the collected bird nests in the dining room centerpiece, her fever for feathered birds waned and a fever for furry creatures waxed. Meanwhile, your other child is deep into collecting bacteria from teeth and in a related but separate experiment, growing bacteria in numerous jars containing teeth soaking in saliva moistened foods. Every new interest is a fever.
Every endeavor is serious.
At times there are several at once. A sense of humor helps. So does a low sensitivity to foul odors. Remind yourself that the normal world does exist - somewhere out there. They run full speed ahead then shift suddenly to full stop.