Once upon a time a colleague messaged me about some minutia regarding the assignment I was currently attending. I wanted to reply to her with that thumbs up emoji I had seen people using. But I couldn't find it and eventually gave up, and instead responded with a cow emoji, concluding that it'd show that I'd read the message.
I have since found the thumbs up, but due to usage history the cow is placed higher up, so I keep using it whenever a message needs a response where the actual contents doesn't matter.