how tall is the ...?

[This problem is adapted from the Chinese elementary mathematics curriculum. You can see the problem in its original form below.] Place the cat on the table and the turtle on the floor. Note the difference in height between the top of the cat's head and the top of the turtle's back. Now place the turtle on the table and the cat on the floor. Again note the difference in heights. With only these two pieces of data can you deduce the height of the table? the cat? the turtle? What questions could/would you put to your students based on this applet?
Puzzle adapted from Chinese elementary curriculum