Exeter Riddle 37

This is the 37th riddle from The Exeter Book.

Translation

I saw a creature     with its stomach behind
And greatly swollen.     A servant grasped it,
A mighty man,     whose muscles laboured
'Til that which filled it     flew from its eye.
It did not die,     disgorged of it contents
Given to others,     but got back again
Health to its breast,     Its breath hallowed.
From its father     it formed a son.

           Translation by Conrad Leviston.

Answer

bellows