Visitor sends text message to the Zoo.
The message is interpreted and forwarded to the radarboy server.
The relevant animal and action is invoked and a response is written to the database.
SMS confirmation reply to sender.

P.S.
If a visitor approaches the animals too closely, the motion sensor webcam triggers a response from an animal.

Variables
Each animal is similar to its real life counterpart in terms of age, weight, hunger and lifespan.
Factors determining the animal's health are hunger, happiness and poo (how clean or dirty its cage is) - these help determine its health rate which affect its health overall.
Other factors that influence the animal are sleep, age and the Rand/Dollar exchange rate. If it's up, the animals are happy, if it's down, they're depressed.

Bonus
Top trumps to take home.

> > > > > > > > > > > > > > >

DOCUMENTATION  |  SPECIFICATIONS