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

Try it here


f=
  (a,b)=&gt;{for(c='chicken',s=[j=0,b,...A=a.split`
`.map(m=&gt;m.split(c).length-1)],i=A.length+2;j&lt;A.length;([_=&gt;s[++i]=c,_=&gt;s[--i]=s[i]+s[i+1],_=&gt;s[--i]=s[i]-s[i+1],_=&gt;s[--i]=s[i]*s[i+1],_=&gt;s[--i]=s[i]==s[i+1],_=&gt;s[i]=s[2+j++]?b[s[i]]:s[s[i]],_=&gt;s[s[i--]]=s[i--],_=&gt;j+=s[--i]?s[--i+2]:0,_=&gt;s[i]=String.fromCharCode(s[i])][s[j+2]-1]||(_=&gt;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!')
&lt;pre id=i&gt;