To defeat the demon Hiranyaksha, Lord Vishnu took the form of a mighty boar. In this form Vishnu defeated Hiranyaksha.
Next, Vishnu became a sow, and as a sow Vishnu gave birth to piglets, nursing them contentedly. It felt so good!
The gods petitioned him. "Vishnu, give up that body and return to heaven."
But Vishnu refused. "I'm staying here. I like this body."
Finally Lord Shiva came to free Vishnu from his incarnation. "Don't you remember who you are?" he said, and he struck Vishnu with his trident, destroying the sow's body.
Only then did Vishnu return to heaven.
Inspired by: Tales and Parables of Sri Ramakrishna
Notes: This is story 32 in the book. The usual story says that the god Vishnu took on a boar avatar form, Varaha, to defeat Hiranyaksha. But there is also a she-boar legend, Varahi, and in this story Ramakrishna blends the two traditions. Compare also the story of how Shiva had to take form as Sharabha in order to get Vishnu to give up his Narasimha (Man-Lion) avatar form.