Physical interaction is when you preform a action to/with/near and object, then the object determines what action you took and what the appropriate response is, and finally the object communicates that response back to you. A good physical interaction is one that takes place smoothly, can analyze complex input, and produces a meaningful result.
I do agree with Crawford’s that language is a large part of why interactivity is so hard to achieve. It simply makes sense when I think about the words and phrasing myself and others use to communicate ideas, along with thinking on the trouble with translating foreign words or conversing in a foreign language — how hard it is to communicate an idea when there isn’t the correct word, or too little an amount words or too many, for it.
Berry College Physical Computing 2017 