How I wish I didn't.
Inside were the remains of a long-deceased and much-desiccated mousie. Poor little thing must've jumped in and not been able to get out. Not a pleasant way to go. Also, ick.
That travel mug is now in a small plastic bag, tied up, and that plastic bag is in the garbage. And I've washed my hands about 89 times.
Jibblie jibblie jibblie...