How much trust should we place in the San Francisco Zoo?

Every year since we started having kids, Spring has meant time to start visiting the San Francisco Zoo. Even though their adopt an animal program really chaps my hide, we still really enjoy going. We're members and we usually go on the monthly Member Day so we can get in early. We like to get our free ride on the carousel, hit the train before the crowds come out, and have an early lunch before it gets too crowded and hot. I know what we need to do when, so we get in and out with few child or adult meltdowns. I really thought I had our zoo trips all scoped out, but then last Christmas day everything changed.