diff --git a/README.md b/README.md
index df7096e..25a8a61 100644
--- a/README.md
+++ b/README.md
@@ -96,7 +96,10 @@ cmd = readlineSync.prompt();
 ```
 
 ## Note
-+ The your Node and OS may not support interactively reading from stdin. The stdin interfaces are different by platforms.  
+
+### Platforms
+
+The your Node and OS may not support interactively reading from stdin. The stdin interfaces are different by platforms.  
 If in those platforms, an error is thrown.
 
 ```js
@@ -108,6 +111,19 @@ try {
 }
 ```
 
+### Reading by shell
+
+readlineSync tries reading from stdin by shell if it is needed. And, it use "piping via files" for synchronous running.  
+As everyone knows, "piping via files" is no good. It blocks event loop and a process. It may make your script be slow.
+
+Why did I choose it? :
+
++ The best solution is [child_process.execSync](https://github.com/joyent/node/blob/master/doc/api/child_process.markdown#child_processexecsynccommand-options) in core modules of Node. But it is not supported by current version.
++ The good modules (native addon) for synchronous execution exist. But node-gyp can't compile those in some platforms or Node versions.
++ I think that the security is important more than the speed. Some modules have problem about security. (It don't protect data.) I think that the speed is not needed usually, because readlineSync is used while user types keys.
+
+Someday, I may rewrite readlineSync to use child_process.execSync, or safety module.
+
 ## Release History
  * 2014-07-13			v0.4.3			fixed #6: Crypto input data.
  * 2014-07-12			v0.4.2			`setPrompt()` and `setEncoding()` return current value.
diff --git a/lib/readline-sync.js b/lib/readline-sync.js
index 524308d..8d1c259 100644
--- a/lib/readline-sync.js
+++ b/lib/readline-sync.js
@@ -78,6 +78,8 @@ function _readlineSync(display, options) {
 
 function _readlineShell(noEchoBack) {
   // piping via files instead of execSync (node v0.12+)
+  // https://github.com/joyent/node/blob/master/doc/api/child_process.markdown#child_processexecsynccommand-options
+  // see README > Note
   var shellPath, args, shellStdout,
     pathStdout = getTempfile('readline-sync.stdout'),
     pathStatus = getTempfile('readline-sync.status'),
diff --git a/package.json b/package.json
index 356ccde..2a4591b 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "readline-sync",
   "description": "Synchronous Readline",
-  "version": "0.4.5",
+  "version": "0.4.6",
   "homepage": "https://github.com/anseki/readline-sync",
   "author": {
     "name": "anseki"