You know this feat whereby you roll your tongue's sides inwards?

Books and MY TUTOR have said it's genetic inheritance. Yet, i've remembered clearly i wasn't able to do it when i was younger, and i had to "train" myself to do it...

So just now i went to ask my mum and sis and they can't do it... and my dad initially wasn't able too until he tried and tried and was able to pull it off slightly.

Hmmm...