doubt
訝 centers on a state of questioning or suspicion: doubt, wondering whether something is true or trustworthy.
訝 combines 言 (speech) with 牙, which likely contributes the sound and may suggest a bared fang, hinting at a questioning or suspicious attitude.
Words (言) that show teeth (牙) like a suspicious snarl: when someone speaks with a hidden bite, you doubt their intentions.
For ガ, imagine a guard (ガード) eyeing you with doubt, his words sharp as fangs: guard -> ガ.
puzzled; perplexed; quizzical; dubious; suspicious
suspicious; doubtful; dubious; questionable; fishy
quizzical; puzzled; inquisitive; suspicious; doubtful
to be suspicious of; to be doubtful of; to be dubious of
to wonder; to puzzle oneself about; to feel anxious about; to suspect; to doubt