Walter Bishop just loved April Fool's Day, for he loved pranks. And as this year, Belly was with him, however in Olivia's body, he was planning his best prank ever, if he said so him self. Belly was expecting one, for he had been the subject of the many in the past.
All day in the lab, Bell was careful and alert, or rather, more so than he was normally. He didn't go near Walter, or eat in front of him, or touch object that had just been touched by him, preferring to wait until Peter or Astrid had made sure it was safe.
At the end of the day, Bell asked Walter what the prank was.
"Ah, y-you see, Belly, there was no prank," Walter said with a chuckle, "But as you expected one, it was, in a way."