The spelling of the word "REEP" can be explained using the International Phonetic Alphabet (IPA). The sound of the word starts with /r/ which is a voiced alveolar trill. This is followed by the sound /i:/ which is a long vowel sound that is pronounced with the mouth slightly open and the tongue raised. Finally, the sound /p/ is an unvoiced bilabial plosive, which is produced by blocking the airflow with the lips and releasing it suddenly. Together, these sounds create the spelling of "REEP".