It could be the app you are using, or the operating system you are on, there are a number of factors that influence which set of emojis you are looking at.
But within any particular set, you most likely encounter emojis that are so similar to each other that you can easily animate between them. And no, this is not another poop ice cream story. This happens to be about the Expressionless Face 😑.
To quote Emojipedia, 😑 is …
A yellow face with flat, closed eyes and mouth. May convey a sense of frustration or annoyance more intense than suggested by 😐 Neutral Face, as if taking a moment to collect itself.
Did you spot the Neutral Face reference? Well, in an idle brain moment, I created a CodePen, ending up with a neutral face that appears to be blinking.