Sanskrit joke cum poem - why Ganesha sneezed?

सानन्दं नन्दिहस्ताहतमुरजरवाहूतकौमारबर्हि-

त्रासान्नासाग्ररन्ध्रं विशति फणिपतौ भोगसङ्कोचभाजि । गण्डोड्डीनालिमालामुखरितककुभस्ताणडवे शूलपाणेर्वैनायक्यश्चिरं वो वदनविधुतयः पान्तु चीत्कारवत्यः ॥ (मालतीमाधवम्)

भवभूति -

As Shiva dances his evening dance, Nandi plays the drum. Mistaking the drum's sound for thunder, Kumara's peacock comes close. Afraid of the peacock, Shiva's serpent searches for a hole to hide. And enters Ganesha's trunk. Shaking his head, Ganesha lets out a sneeze.

May this vigorous shaking of head, accompanied by a sneeze, protect us.

..श्रीशङ्करराजरमणः।