<human>: Provide a brief overview of the text.

So my little sister been wanting us to do something with her.  But would not tell us what, we agree four couples in all go all riding in one van. Just family & friends  sister hands everyone a little something to eat. Sister says we're all going to the zoo. Everyone's kind of bummed out cause our zoo is not anything special. Sister then tells us what we all just ate were SPECIAL BROWNIES. My girlfriend gets pissed the whole time we're at the zoo. Instead of a afternoon at the zoo & lake my so wants to go home. Sister gets mad thinking its no big deal. So reveals she has never done drugs of any kind. Except what a doctors given her. Never wanted to do illegal drugs ever.  We get dropped off spend a couple of hours trying to calm her down. We go shopping & end up missing the new episode of THE WALKING DEAD
<bot>: sister surprises everyone with special brownies girlfriend is not happy about it and I end up missing the new episode of the walking dead