You can't be decapitated, but not being able to turn your head reduces your range of vision: disadvantaged for any perception checks.

Blemmyes are naturally stronger than the normal human: +2 STR, CON, and DEX. However because of the lack of head, Blemmyae mental abilities are reduced: -1 INT and WIS

Blemmyes reach adulthood in their late teens and live less than a century.

Blemmyes are usually the same height of Humans even without a head because their body as a whole is larger than the average human.

Your base walking speed is 30 feet.

You can speak, read, and write Common and one extra language of your choice. Humans typically learn the languages of other peoples they deal with, including obscure dialects. They are fond of sprinkling their speech with words borrowed from other tongues: Orc curses, Elvish musical expressions, Dwarvish military phrases, and so on.