Leo could remember a full moon on Halloween from years ago. They'd gone topside and Raph spent the night scaring Mikey about werewolves. 

It started as a joke to scare Mikey, but Leo would be lying if he said that he hadn't been worried as well. After Donnie pointed out that werewolves were probably real; since they would be mutants like them, he was sure that Raph was nervous to.

Many Years later, miles away, in South America. Leo stared up at the full moon, listening to the wolves in the distance; Wondering if his brothers even remembered that night.