It's hard to tell in the video, but the third character, よ (yo), is a subscript to the previous character, ち (chi), which blends the two into a single, different letter, ちょ, or "cho." There are several letters in which や (ya), ゆ (yu), and よ are subscripted to "i" letters like に (ni), り (ri), and ぎ(gi), to make letters like にゃ (nya), りゅ ("ryu," like the Street Fighter guy!), and ぎょ (gyo). Take a look at the attached comic strip and you'll see the words "こちょ こちょ こちょ" written vertically in the panel where the tickling occurs. Hope that helps, and I apologize if I told you things you already knew!