This is the "Thai Alphabet" taught in schools.
In Thai only certain consonants can be combined. Any combinations not listed here will be pronounced with an "invisible o" in between.
ห Consonant Combinations
ห is silent and only changes the class of the following consonant to high
อ Consonant Combinations
อ is silent and only changes the class of ย from low to mid
ร Consonant Combinations
ร is silent
Other Possible Combinations