poor as a church mouse

The story

Alteration of earlier hungry as a church mouse, from the fact that Catholic and Orthodox priests are called to scrupulously prevent any crumb of the sacrament of Eucharist (the bread which is understood to be Christ's body) from falling on the altar or to the ground, meaning that church mice had no crumbs to feed on. This phrase seems to be a corruption of the even earlier expression “as quiet as a church mouse” from the 1300s.