One of the lions at the Denver Zoo is a 13-year-old male named Krueger.
Getting Krueger's attention is tough.
One thing he is interested in right now is Natal, a 12-year-old lioness who is in heat, but there is one other thing Krueger gets excited about.
It's Obsession for Men by Calvin Klein.
When the cologne is sprayed on the exhibit enclosure or on a surface in the exhibit, Krueger immediately goes over to the spot and rubs his cheek on it.
Emily Insalaco, curator of behavioral husbandry at the Denver Zoo, is not entirely surprised.
"Perfumes, cologne, they work the same for us as they do for the animals. They contain pheromones, and supposedly we're supposed to be attracted to people who are wearing these perfumes because of those pheromones. Well the animals use pheromones for that type of communication too, to let each other know they're available, that they're cycling, they're in the right season, they're interested," she said.
What Insalaco cannot explain, is why Krueger and some of the other big cats at the Denver Zoo like Obsession in particular.
"One of the things they do like is cinnamon, and I did notice there was a cinnamon oil that's in Obsession for men, I have no idea if that's why," Insalaco said. "No catnip in there."
She says just like people, not all big cats like the cologne.
"You saw Natal and Krueger react to that, but Tawny and Baby, two of the other cats in that exhibit, didn't react at all. So you had a 50-50 reaction. Some scents you're going to be very attracted to, some scents not so much," Insalaco said.
Insalaco says the lions rub themselves on the spot sprayed with Obsession for three possible reasons.
They simply like the smell, are trying to gather information from the scent, or deposit their own scent on the same spot.
"That cheek rubbing behavior that you saw, that was them picking up that pheromone information, and that's what they would do in the wild," Insalaco said. "They sense something, they might rub their cheek, it helps them pick up some of that information, also deposit some of their own information. That's what you were seeing them do with the pheromones in the cologne. It's just hormones. It's chemical information that let one another know that 'yes I'm interested' or no 'I'm not interested.' 'Yes I'm ready. 'No, I'm not ready.'"
Insalaco says spraying Obsession in the lion exhibit has a purpose.
It encourages their natural behavior of cheek rubbing and provides them changes in their environment to keep them stimulated.
She says the Denver Zoo started buying Obsession for men for the zoo felines after the Bronx Zoo in New York conducted research showing that big cats like the smell.
The Bronx Zoo tested more than 20 perfumes and colognes, and Obsession was the winner.
The discovery has led to scientists being able to better study big cats in the wild, since they can lure them towards cameras and other research equipment by spraying an area with the cologne.
Insalaco says she is not sure Obsession would go over well with domestic cats.
She also can't guarantee that men will attract more women if they wear the cologne.
"That's a personal choice. Like I said it was 50-50, so they're going to have to ask their girlfriends," Insalaco said.
She says the Denver Zoo has not contacted Calvin Klein to let him know what a hit his original scent is with the lions.