Love this one:
The head scratcher: While identifiers in many other languages are usually case sensitive, in PHP function names (as well as class and method names) are case insensitive. To really confuse developers, variable names, constants and class properties in PHP are case sensitive.
The reason: Most likely an artifact of PHP’s organic development from a set of CGI scripts to a full-fledged programming language.
Quotes: “Well, it's PHP, you shouldn't be suprised.” Grzechooo