Interesting indeed!!
0x63 is the ASCII code of 'c'.
0x64 is the ASCII code of 'd'.
Why am I missing the ASCII codes for 'a' and 'b'?
Serial.println('abcd', HEX); //shows: 0x6364; why not: 0x61626364
Serial.println('cd', HEX); //shows: 0x6364
Serial.println('ab', HEX); //shows: 0x6162 = ASCII codes of 'a' and 'b'.