hè is the formal, written reading - lives mostly in two-character compounds about deliberate intimidation: 恐吓 (threaten), 恫吓 (menace), 威吓 (cow into submission). The standalone verb hè barely appears in speech; learners meet it almost entirely through these compounds.
memory
Two readings, two registers. xià = spoken scare (你吓我一跳 = you startled me). hè = written intimidate (恐吓 = legal-language 'criminal threat'). Picture xià as a friend going BOO behind you; hè as a prosecutor reading out the charge of 恐吓罪.
Left mouth - the indexing radical. Anchors 吓 as something done with the voice: a sudden shout to startle someone. From that vocal jolt came the modern senses to scare and to threaten. Same vocal family as 叫, 喊, 吼.
Right 下 supplies the sound for the xià reading. The down-arrow shape also adds a faint semantic hook: a startled person ducks down or sinks. Same phonetic in 虾. For the hè reading (恐吓, 威吓), the sound link has drifted - the traditional form 嚇 took its phonetic from 赫 instead.
