I mean, come on, there's got to be a moment where the Yeerk and unvoluntary host agree with eachother, maybe without realizing it.
Aka, you know how maybe when you were in school or work, and something random, funny or weird will happen and you'll just turn around to the nearest person and go, "O...kay, that was strange..." whether or not you know them?
For example in the books: In The Reaction, when Rachel accidently changes her feet into bear's paws and she tells Chapman their actually fancy shoes?
There's an awkward pause until "Chapman" (aka Yeerk) says, "The things you kids wear..." you wonder if afterwards the Yeerk was like, "Well, that was just plain weird." and perhaps Chapman could have said, "Yeah, you'll find that with human kids." or something...
Do you think that would ever happen in the Animorphs universe?