diff --git a/.travis.yml b/.travis.yml
index 1ea0074..9f7930e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@ dist: trusty
 language: rust
 cache: cargo
 rust:
-  - nightly
+  - beta # Change this to stable when Rust 1.31.0 is out
 branches:
   only:
   - master
diff --git a/book.toml b/book.toml
index f34accd..f3bcb0e 100644
--- a/book.toml
+++ b/book.toml
@@ -5,3 +5,7 @@ description = "Rust 程序设计语言 简体中文版"
 
 [build-dir]
 destination = "mdbook"
+
+[output.html]
+additional-css = ["ferris.css"]
+additional-js = ["ferris.js"]
\ No newline at end of file
diff --git a/ferris.css b/ferris.css
new file mode 100644
index 0000000..b856d47
--- /dev/null
+++ b/ferris.css
@@ -0,0 +1,33 @@
+body.light .does_not_compile,
+body.light .panics,
+body.light .not_desired_behavior,
+body.rust .does_not_compile,
+body.rust .panics,
+body.rust .not_desired_behavior {
+  background: #fff1f1;
+}
+
+body.coal .does_not_compile,
+body.coal .panics,
+body.coal .not_desired_behavior,
+body.navy .does_not_compile,
+body.navy .panics,
+body.navy .not_desired_behavior,
+body.ayu .does_not_compile,
+body.ayu .panics,
+body.ayu .not_desired_behavior {
+  background: #501f21;
+}
+
+.ferris {
+  position: absolute;
+  z-index: 99;
+  right: 5px;
+  top: 30px;
+	width: 10%;
+	height: auto;
+}
+
+.ferris-explain {
+  width: 100px;
+}
\ No newline at end of file
diff --git a/ferris.js b/ferris.js
new file mode 100644
index 0000000..5d014f3
--- /dev/null
+++ b/ferris.js
@@ -0,0 +1,51 @@
+var ferrisTypes = [
+    {
+      attr: 'does_not_compile',
+      title: 'This code does not compile!'
+    },
+    {
+      attr: 'panics',
+      title: 'This code panics!'
+    },
+    {
+      attr: 'unsafe',
+      title: 'This code block contains unsafe code.'
+    },
+    {
+      attr: 'not_desired_behavior',
+      title: 'This code does not produce the desired behavior.'
+    }
+  ]
+  
+  document.addEventListener('DOMContentLoaded', () => {
+    for (var ferrisType of ferrisTypes) {
+      attachFerrises(ferrisType)
+    }
+  })
+  
+  function attachFerrises (type) {
+    var elements = document.getElementsByClassName(type.attr)
+  
+    for (var codeBlock of elements) {
+      var lines = codeBlock.textContent.split(/\r|\r\n|\n/).length - 1;
+  
+      if (lines >= 4) {
+        attachFerris(codeBlock, type)
+      }
+    }
+  }
+  
+  function attachFerris (element, type) {
+    var a = document.createElement('a')
+    a.setAttribute('href', 'ch00-00-introduction.html#ferris')
+    a.setAttribute('target', '_blank')
+  
+    var img = document.createElement('img')
+    img.setAttribute('src', 'img/ferris/' + type.attr + '.svg')
+    img.setAttribute('title', type.title)
+    img.className = 'ferris'
+  
+    a.appendChild(img)
+  
+    element.parentElement.insertBefore(a, element)
+  }
\ No newline at end of file