If you post a symbol, cleverbot might not recognise it and effectivley crash. It will post a message and then forward you to an error page.
On a Mac, one that works is the apple symbol (alt+shift+k). You will not see it here → ← unless you use a mac. This is the one i used.
Here are some screenshots:
Typing the sign...
The message he sends you:
The page it forwards you to: