Human-model Cylons are virtually indistinguishable from the real thing. Their biology is a match in every way. They can eat, drink, sweat, breathe, sleep, laugh, cry, and even frak. Whether they need to do these things or they’re just faking is anyone’s guess. A lot of colonials hope the physical stuff is real at least, because that would mean they can hurt.
Each of the human model types appears to look the same. All the number ones look like number ones, for instance, and all the number twos look like number twos. They can disguise themselves, but they either can’t change their basic appearance or they choose not to. This is one of the only points in our favor so far. As each one of the twelve is identified, there are fewer chances of another sleeper agent slipping into the fleet. Right now, all they have to do is sneak one of the unknown models onto a ship with a bomb and set it off. Who knows why they haven’t yet. Maybe they value their lives more than we give them credit for. That would be more good news because it means they can fear.
It’s unknown how the Cylons share memories. According to the Conoy model on Ragnar, each one that’s killed simply wakes up in another body somewhere else. Where? Do they wake up on their basestars, back on their home world, or somewhere else? Do they trade information like computers or do they have to talk to each other?
Cylon brains have clearly evolved in the last forty years, though they still use a variant of the original silica technology.