I think it is the heart Hi's but....

We tried to get it to work last night. It's definitely not quantity of "Hi"s. There were people with hearts and we still didn't see the comet though.

To be honest, I think the comet lights up the heart, but I have NO idea what sets off the comet.

is it two people wearing the same article of clothing?

That happened to me the comet sets off when you jump across from the left to the right hill in a certain way