Hi Phil,
Firstly, I understand why you’d ask this question, as yours was a great caption and you scored highly compared to others on the shortlist.
The process for choosing the prize winner is:
- The day before the end of the month, I post a poll on the forum to choose the winner from the shortlist (ten top scoring captions of the month)
- The poll is visible to Contributors (i.e. those who have paid into the prize fund)
- The shortlisted caption with the most votes by 10pm on the last day of the month wins the prize
Reasons for this extra voting stage:
- It’s possible to manipulate the main caption vote by colluding or creating fake accounts. Our mod team has measures in place to spot unfair voting, but we may not catch them all
- It’s only contributors who provide the cash prize fund, so it’s fair they’re the ones to decide the winner. In the past, it was only me that picked the winner, but now there are 22 contributors who do so. Much better!
- Contributors are mostly long-standing captioneers who have read thousands of captions and have a knack at spotting original humour that takes effort and creativity
- Contributors may also use to the final vote to reward people who have managed to get two or more captions into the shortlist (in this case, @John_Harrison had two)
Please don’t take this to mean that your Zebra caption wasn’t original, or that there was any suspicion of unfair voting.
The process isn’t perfect, but I believe it makes sense, and we are always open to new contributors if anyone would like to take part in the final voting stage, and help fund the site so we can continue to offer cash prizes.
In fact we could really do with some more contributors, since we currently only have enough money in the pot to pay out two more prizes this year 
Instructions for contributing can be found here.