(Mental Floss) -- Watching the post parade at this weekend's Kentucky Derby will surely fill some of our heads with dreams of horse ownership.





How did the julep-sipping folks acquire their prized horses? How much is buying a racehorse going to set you back? Are they sound investments?





These are all tricky questions, but let's take a look at a few stories of horse sales that turned out to be winning lottery tickets...and a few that were more dud than stud.





Mr. Prospector becomes a daddy again and again





In 1971, Mr. Prospector was a yearling that fetched $200,000 at auction. When he took to the track, he was good but not great; he won seven of 14 starts but only brought home $112,170 during his career.





Still, in 1980 he sold for $20 million.





What happened? It turns out "Mr. P." was a stud in every sense of the word. While his racing career might not have been the most distinguished, it's tough to argue with his results as a stud.





He sired a winner of each of the Triple Crown races, and his grandchildren and great-grandchildren have been similarly speedy. His sons, grandsons, and great-grandsons have combined to win over 30 Triple Crown races and pull in around $100 million in earnings.





Mr. P.'s Derby-winning son Fusaichi Pegasus fetched $60 million in 2000, and 18 years earlier, another son -- Belmont winner Conquistador Cielo -- sold for $36.4 million.





Mental Floss: Did famous horses get their names?





John Henry drives steel, wins cash





When John Henry, a yearling foaled in 1975, came up for bids at the Keeneland January Mixed Sale, he didn't generate much buzz. He had fairly mundane bloodlines, he wasn't particularly big, and he had a nasty temper -- he got his name from a tendency of smashing steel feed buckets.





John Calloway bought the unheralded gelding for a modest $1,100 investment and hoped he could make a little cash back on the horse.





How did it work out? By the time John Henry retired from racing, he was the top-earning gelding in history with over $6.5 million in career earnings. He won 25 graded stakes races and was racehorse of the decade for the 1980s. Not a shabby return on a $1,100 investment.





The Green Monkey makes a monkey out of bidders





Unless you're a huge fan of the band America, you might not envision shelling out eight figures for a horse with no name. That's exactly what happened in a January 2006 auction at Calder Race Course, though.





When the auctioneers brought a colt who was only known as "number 153" to the auction block, a fierce bidding war broke out. Buyers weren't afraid to open their wallets for a colt that was described as "perfect," and when the hammer dropped the horse went for a record $16 million.





The winning bidders quickly christened the colt The Green Monkey, and excitement to see how the horse would do in races began to build. After all, the colt had run an eighth of a mile in a blazing 9.8 seconds in pre-auction workouts, so anything was possible once he started racing.





The buyers thought they were getting a Triple Crown threat. Instead they got the thoroughbred version of Ryan Leaf. The Green Monkey could never translate his workout speed into actual races, and in his career, he only managed one third-place finish in a measly three starts.





In 2008, his owners retired him from racing to stand at stud. If his progeny enjoy the success that eluded the Green Monkey, he might make some of his substantial purchase price back. It will be tough, though; right now he only pulls in $5,000 as a stud fee.





Mental Floss: 7 things to know about the Kentucky Derby





...But he's in good company





The Green Monkey shouldn't feel too bad. The horses he took the "most expensive colt" record from didn't fare much better.
How much did Green Monkey sell for? who won 112170 How much did Mr. Prospector win? What did Mr Prospector win?
$16 million. Mr. Prospector $112,170 seven of 14 starts
question: How much did Green Monkey sell for?, answer: $16 million. | question: who won 112170, answer: Mr. Prospector | question: How much did Mr. Prospector win?, answer: $112,170 | question: What did Mr Prospector win?, answer: seven of 14 starts