Honestly, the fact that he can sense Spark at all, when the Sense doesn't normally pick up on animals, is going to be enough to get and hold his attention. He wouldn't put it together after the first few meetings of any of the three forms, but he's also a smart kid - once he gets to know one fairly well, it won't take him long to realize they read the exact same to his Sense.

Essentially, if we want this to take a while IC as well as OOC, they might not get to interact closely very often. A team setting would be fine, but one-on-one threads might not get to happen as often.