Kristen Bell spent a good portion of her 31st birthday in tears. The reason? The House of Lies actress’ fiance, Dax Shepard, presented her with the ultimate surprise: playtime with her favorite animal. PHOTOS: Celebs and their pets “The day of my birthday, we’re sitting in the living room and I hear a knock at the door. He says, ‘Your present is here. Why don’t you grab the dogs and go in the back room?’” Bell tells Ellen DeGeneres on her eponymous talk show (airing Tuesday). “I was immediately overcome and I thought, ‘There is a sloth near! There is a sloth here! It’s close! It’s gonna happen!’” VIDEO: Kristen Bell flirts with fiance Dax Shepard Bell explains: “I didn’t know how to process that because my entire life had been waiting for this moment where I would get to interact — I’m serious! — with a sloth.” The Veronica Mars alum assured DeGeneres, 54, that she often gets hysterical when excited. “If I’m not between a three and a seven on the emotional scale, I’m crying,” Bell said. PHOTOS: Lavish Hollywood birthday parties What happened when Shepard, 37, presented his bride-to-be with the sloth named Melon? “I was sitting on my bed, knowing that my sloth is here, and I start to have a full-fledged panic attack. I don’t know how to compete with all this emotion so I just kind of crawl up on the bed and I’m crying so hard,” Bell says. “Dax knocks on the door and he has a video camera and he’s like, ‘Surprise! I want you to come out into the . . . are you alright?!’ And he sees me basically fetal on the bed.” PHOTOS: Celebrity animal charities To see Bell’s hilarious meltdown, watch the video (above) and tune in for the full interview on Ellen (check your local listings).