This made a thought pop into my head. Not sure if this has been discussed before, but: would a Yeerk show up on something like an MRI or CT scan? I mean, what if a host just happened to develop brain cancer or something and had to go to the hospital.
Yeah, I know they had controllers everywhere (cops, hospitals, schools) but let's assume they get some bad luck and wind up with a normal doctor.
This picture made me laugh, by the way.