一則羞 Half Ashamed And Half Alarmed
假春嬌道：「大王，拿鈴子來，等我也與你捉捉虱子。」那妖王一則羞，二則慌，卻也不認得真假，將三個鈴兒遞與假春嬌。假春娇道：「大王，拿铃子来，等我也与你捉捉虱子。」那妖王一则羞，二则慌，却也不认得真假，将三个铃儿递与假春娇。
逐句解 Line by line
The false Chunjiao said, "Great King, hand over the bells and let me pick the lice off those too."
The whole chapter turns on this sentence and it is phrased as a chore. 也 — those too — makes the bells sound like one more item of clothing. 子 in 鈴子 and 虱子 is the light noun ending zi.
The fiend king, ashamed in the first place and flustered in the second, could not tell true from false,
一 keeps yī here rather than shifting: 一則…二則… is the counting-off construction, in the first place and in the second, and the character is doing the work of an ordinal. 得 is dé, the fixed ending on 認, to recognise.
and handed the three bells to the false Chunjiao.
Ten characters, and the treasure changes hands. 將 is jiāng, the disposal marker, putting the bells in front of the verb that gives them away.
Ask plainly and you get it. The false maid does not scheme, distract or steal — she asks for the bells out loud, in front of their owner, and gives a reason so mundane that refusing would be odder than agreeing. The lice have to be picked off those too.
一則羞，二則慌 is a precise little diagnosis. Two reasons, counted off, and neither of them is suspicion. He is embarrassed about the lice and rattled by the burglary, and between the two of them he has no attention left for the maid with her hand out. The construction keeps 一 at its full tone, because it is doing the work of firstly rather than of one.
卻也不認得真假 is the narrator getting ahead of the story. There is nothing false to recognise yet — the bells he hands over are the real ones. The phrase is there to tell you what is about to happen.