Re: tori vs. dori
One hand = katate
Grab = toraeru (tori)
Japanese will often change the syllable of the second word for easier pronunciation. i.e. flower = hana, ikibana is flower arranging. 'h' changes to 'b' since they are related in hiragana their phonetic alphabet. Same with 'to' and 'do'.
I asked my Japanese friends and they say they just know.