For years, many have tried and failed to answer one of life's greatest questions: What makes Kanye West smile? On Thursday, Kim Kardashian West gave away the much-sought-after answer for free, revealing via her Instagram and Snapchat Stories that one thing guaranteed to make her notoriously stoic husband crack a smile is a day spent with his kids and a few friendly animals.

Kardashian West documented her family's trip to the San Diego Zoo on social media, tagging the zoo's Instagram account in several of the photos and videos she posted Thursday evening. The Wests' firstborn, 4-year-old North, was featured prominently in the mom of three's uploads: In snaps taken throughout the family outing, she feeds an elephant some greens, flashes a peace sign in front of the elephant's cage, sports a huge grin while standing next to a hippopotamus, and peeks at a pair of penguins with her mom. Kardashian West closed out her visual recap of the day with an adorable photo of West beaming while crouching down to cuddle with 2-year-old son Saint. Notably absent from the day's fun was Kimye's 2-month-old daughter Chicago, presumably because a loud and germ-filled zoo isn't an ideal hangout spot for a newborn.

kimkardashian/Instagram
kimkardashian/Instagram
kimkardashian/Instagram

The Kardashian-Jenner clan are longtime fans of the San Diego Zoo. Not only have Kim and older sister Kourtney Kardashian taken their kids to the zoo many times before, but during one such occasion, momager Kris Jenner also revealed that the popular attraction has held a special place in her heart for several decades. Back in August 2014, Jenner shared a photo of her and North petting a giraffe at the San Diego Zoo on Instagram, sharing in a long-winded hashtag that her own first birthday party had taken place at the zoo.