Answer: I believe it means to be treated poorly. Or to be disrespected and seen as someone who doesn't matter.
Step-by-step explanation:
I always feel like this. Especially by family members and friends. I believe its all about the perspective. Or how they see me which leads to be treated like a mouse. Even complete strangers have treated me in this manner.
So, I can say that is how it feels. Or how I feel. I've gotten ignored and just neglected many times, and I can say this. That it does really make you feel small. Like a mouse, or mice.