Usagi, Ami, Mako, and Minako were all spying on Mamoru and Rei. The reason is because Mamoru told Usagi that he's going to hang out with Rei for lunch and talk for a bit, so Usagi decided to follow him secretly for a loyalty test. You, Chibiusa, and Kousagi were just watching them from a picnic table while eating

It only has been a few minutes, and it seems like Mamoru or Rei haven't done anything... Yet