Delayed or unusual speech patterns (many autistic children, for example, memorize video scripts and repeat them word for word with the precise intonation as the TV characters)
High pitched or flat intonation
Lack of slang or "kidspeak"
Difficulty understanding tone of voice and body language as a way of expressing sarcasm, humor, irony, etc.
Lack of eye contact
Inability to take another's perspective (to imagine oneself in someone else's shoes)
Engage in repetitive behaviors and ritualized activities, ranging from lining up items to following a rigid routine
Have one or a few passionate interests
Have difficulty in making and keeping multiple friends
Prefer activities that require relatively little verbal interaction