My favorite is that two obviously different hexadecimal values in strings (e.g. checking password hashes) can be "equal" with the weaker == comparison.
This occurs if PHP thinks both strings could be numbers in scientific notation. "0e123" == "00e45"
Note that PHP also has a JavaScript-style triple-equals comparison, which does not attempt type conversion and does not exhibit this bizarre behaviour.
This occurs if PHP thinks both strings could be numbers in scientific notation. "0e123" == "00e45"