Kate Chastain’s Son, Sullivan, Has Reached a “New Milestone” (PHOTOS)

Kate Chastain's son, Sullivan Cay, is already an expert at making himself laugh, and he has found a brand new way to do it. The Below Deck alum is constantly gushing about her little boy, and his newest milestone — making a razzing sound — might just be his cutest yet.

Kate took to her Instagram Story earlier this week, where she posted the sweetest video in which she's holding Sullivan, who was laughing hysterically. In the video, Sullivan can be seen with his face nuzzled in his mom's neck, making a raspberry noise against her, which he thought was so hilarious. Each time Sullivan made a razzing noise against Kate, he looked at her, which made her laugh. Throughout the video, the little boy is cuddling against his mom, looking at her for approval, and giggling along the way.

"New milestone," she wrote over the video. His smile throughout it all, captured in the following snapshots is too cute for words.

Kate Chastain reveals an update on her son, Sullivan
This new skill is just another way that Sullivan has been able to make himself crack up. Kate took to Instagram on Jan. 31, where she revealed that Sullivan can now laugh on command. She first posted a video of him sitting on the couch, blinking hard, and letting out a small chuckle. In the second slide, Sullivan can also be seen wearing an adorable green and orange matching set, showing he has a serious sense of style, too.

"His new thing is on purpose LOLing," she captioned the post alongside a joy emoji.

Several Bravolebrities took to the comments of the post, where they left the sweetest messages for the little boy. "So cute!!" The Real Housewives of Beverly Hills' Kyle Richards, wrote.

"Omg his little outfit on the second pic!!!" Below Deck Mediterranean Season 5 alum, Jessica More, added.

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Not only can Sullivan laugh and make a razzing noise, but he's also pretty much a genius. Kate spoke with The Daily Dish in January, where she shared a major update on how he's been doing. "Lately, he can count to ten," she said. "He knows the phonetic alphabet, but he's always counting to ten...[He] loves the letters."

Sullivan has even started developing some serious personality on him. "He has learned 'No' recently and what it means and that he can use it," she noted. "So that's been an interesting new development. I'm trying to replace it with please, but we're not quite there yet. But, with time, I'm sure he'll get there."

See what else Kate had to say about Sullivan and her new Florida home here.