Most phonologists working with the English language have to explain that many vowels in English (specifically /i,e,o,u/ aka “long e, long a, long o, long u”) are actually pronounced as diphthongs in an U.S. English accent (actually all English accents, but details vary a lot).
For instance, the Spanish word “Rico” which is pronounced as [riko] in Spanish will come out something like [ɾijkow] in U.S. accented English or even [ɾijkəw]/[ɾijkew] in Baltimore. This is when a language teacher might try to get Anglo students to “use pure vowels” instead of our diphthongs.
The problem is that English speakers do this diphthong trick unconsciously and often have a hard time hearing the difference, unless they’ve got a good ear or had LING 100.
BUT… the theme song from the classic TV show The Addams Family actually takes advantage of this quirky to produce this interesting rhyme in the second verse

Their house is a museum
Where people come to see ’em
They really are a scre-am (scre’um)
The Addams Family.

–http://www.lyricsondemand.com/tvthemes/theaddamsfamilylyrics.html

The song writer did notice the hidden diphthong in scream [skriijm], then managed to stretch it out even further to [skriəm] in order to make a rhyme with museum and see’um. An awful pun, but one that’s very informative.