Six-month-old rolly polly

Emma turned six months old yesterday. She celebrated the occasion by figuring out how to roll from back to tummy and doing it four times! Wow.
She now not only reaches for toys/objects but will twist and turn in order to grab them and pull them to her face for closer inspection.
Lately she has developed a habit of screeching which is wretched and we're hoping to figure out how to prevent it.
Even having moved, she sleeps great. Typically sleeps about 9 hours a night and takes around 4 naps including a nice 2-3 hour late afternoon nap which is my favorite. She usually wakes up babbling/talking which is adorable and much preferred to crying.
I can never be certain if she will cry or smile at strangers - it seems to depend on their method of approach but more so her mood at that time. She does better, usually, when they don't come too close or talk to her.
She weighs 15 1/2 pounds, measures 26 1/2 inches long, and has managed in the last two months to increase her head size from about 50th percentile to 85th. Ha. The nurse even double checked the head measurement.
She was a super trooper today and only cried for a few seconds after getting shots today.
Emma is a seriously good baby and I am glad she is able to do more to entertain herself while still not mobile. :)
Pictures to come later this week (hopefully).