Unlockables
Items

Unlockable ............... How to Unlock
Flower Arch .............. Complete all scenarios in Troubled Zoos campaign
Flowerpost ............... Complete all scenarios in Zookeeper in Training campaign
Gilded Panda Statue ...... Complete all scenarios in The Mysterious Panda campaign
Globe Statue ............. Complete all scenarios in The Globe campaign
Mysterious Panda Campaign Complete all scenarios in Conservation Programs campaign
Sundial Statue ........... Complete all scenarios in Prevent Animal Abuse campaign

Jungle and African themes

You need to complete five photo safari challenges and five game challenges to unlock them.
Unlockable ............... How to Unlock
African theme ............ five game challenges
jungle theme ............. five photo challenges complete

Glitches
Make people repay to enter zoo

To make people repay to enter zoo simply pick them up and put them outside the gate and they will repay. Note if someone is leaving your zoo and you do this they will not come back in and they will walk out.

Secrets
Run in Zoo Guest Mode and Photo Safari Mode

Since left-clicking the mouse makes you walk in Zoo Guest and Photo Safari Mode, and so does W or Up, you can walk twice as fast (aka run) by holding two of these.

Run in Zoo Keeper mode

If you hold down the left mouse button and the up arrow key you can run in Zoo Keeper and Guest mode.