why does Lennie have the dead mouse? why does George take it away?

Lennie likes to hold and pet soft things, and to him...... the mouse is perfect and just the right size for traveling. Unfortunately, Lennie is too rough when petting and kills the mouse, but he still likes to touch its fur, so he keeps it. George knows the mouse might carry a sickness and start decomposing, That mouse ain't fresh Lennie....