QSI: "The Significance of The Ritual of Salat: Why We Turn Toward the Ka'aba" 4

Narrated Abu Huraira:

Allah's Messenger (?) said, "My similitude in comparison with the other prophets before me, is that of a man who has built a house nicely and beautifully, except for a place of one brick in a corner. The people go about it and wonder at its beauty, but say: 'Would that this brick be put in its place!' So, I am that brick, and I am the last of the Prophets." 

The common word for “brick” is “Tubah”. The root of the term in the hadith for brick is the same as for “milk” [Laban} - [Labinah]. 

What’s the relationship between “Milk and Brick”?