Write a chicken interpreter!

Javascript ES6, 398 bytes

By far the longest golf I have ever done, I'm sure this can be improved but my brain doesn't recognize anything other than chicken at this point.

(a,b)=>{for(c='chicken',s=[j=0,b,...A=a.split`
`.map(m=>m.split(c).length-1)],i=A.length+2;j<A.length;([_=>s[++i]=c,_=>s[--i]=s[i]+s[i+1],_=>s[--i]=s[i]-s[i+1],_=>s[--i]=s[i]*s[i+1],_=>s[--i]=s[i]==s[i+1],_=>s[i]=s[2+j++]?b[s[i]]:s[s[i]],_=>s[s[i--]]=s[i--],_=>j+=s[--i]?s[--i+2]:0,_=>s[i]=String.fromCharCode(s[i])][s[j+2]-1]||(_=>s[++i]=s[j+1]-10))(j++));return /[^chicken \n]\w/g.test(a)?0:s[i]}

I will edit the explanation in when my brain starts functioning again. Here's a slightly ungolfed version for now.
Outputs a falsey value (0) for everything which isn't chicken

(a,b)=>{
    for(c='chicken',s=[j=0,b,...A=a.split`
    `.map(m=>m.split(c).length-1)],i=A.length+2; // loop init
    j<A.length; // loop condition
    ( // everything else
        [
            _=>s[++i]=c,
            _=>s[--i]=s[i]+s[i+1],
            _=>s[--i]=s[i]-s[i+1],
            _=>s[--i]=s[i]*s[i+1],
            _=>s[--i]=s[i]==s[i+1],
            _=>s[i]=s[2+j++]?b[s[i]]:s[s[i]],
            _=>s[s[i--]]=s[i--],
            _=>j+=s[--i]?s[--i+2]:0,
            _=>s[i]=String.fromCharCode(s[i])
        ][s[j+2]-1]
        ||(_=>s[++i]=s[j+1]-10)
    )(j++)
);
return /[^chicken \n]\w/g.test(a)?0:s[i]}

Try it here

f=
  (a,b)=>{for(c='chicken',s=[j=0,b,...A=a.split`
`.map(m=>m.split(c).length-1)],i=A.length+2;j<A.length;([_=>s[++i]=c,_=>s[--i]=s[i]+s[i+1],_=>s[--i]=s[i]-s[i+1],_=>s[--i]=s[i]*s[i+1],_=>s[--i]=s[i]==s[i+1],_=>s[i]=s[2+j++]?b[s[i]]:s[s[i]],_=>s[s[i--]]=s[i--],_=>j+=s[--i]?s[--i+2]:0,_=>s[i]=String.fromCharCode(s[i])][s[j+2]-1]||(_=>s[++i]=s[j+1]-10))(j++));return /[^chicken \n]\w/g.test(a)?0:s[i]}

i.innerHTML = f(`chicken chicken chicken chicken chicken chicken chicken chicken chicken chicken chicken
chicken chicken chicken chicken chicken chicken
`, 'Hello world!')

<pre id=i>