You can communicate with wall-kind inside lockers

[phart]

I don't know how often this would come up in normal gameplay, but what I did was the following.

1. Get in a locker
2. Be screamed at by a nearby living wall of flesh.
3. The first message received should be just a normal scream, but underneath it should be a message like "living wall: all life is suffering, please kill me and end this horrible mockery of an existence, all hope for a happy life has been RCD'd right out of me and left me as nothing but a huge architectural husk. A empty husk of a structure is what is left of my soul.", or something like that.

I'm not sure about other containers, but it would stand to reason that they would act similarly.

[Ed Venture]

No idea if this was ever fixed, but I remember being a monkey who need a ID change and communicated with the HOP but getting in a locker and speaking to him while in it. It seems lockers are universal translators.

[Walrus]

I can also recall monkey/human communication with sleepers as well.

[Vunterslaush]

Fun fact: You can understand monkeys in a pod as a human.