If says "listen" before listing the items, the third is a wombat.
Everybody plays the wombat game in a different way (well, not EVERYBODY).
You just need a nimble mind.
First, I'm sure everybody has tried this, but you have to listen VERY CAREFULLY. Here is an example:
P1-Okay, if that chair is a wombat and it had a baby wombat with that computer, is the computer a wombat?
P1-You're wrong. Let's try again. If that chair is a wombat and it had a baby wombat with that computer, is the computer a wombat?
P1-Again, you're wrong.
Did you notice anything? In this case, it's the "okay" in the beginning of the sentence. When P1 said the word "Okay," the computer was a wombat. When P1 didn't say "okay" the computer was not a wombat.
But it doesn't just have to be "okay." Others might say something else, or they might tweak the rules a bit, so you just have to listen carefully.