影视英语口语:soap bubble

“soap bubble”在英语口语里表示什么？

本义：肥皂泡
引申义：幻象

素材来源：《墨水心》
剧情简介：
莫特是一个修补书籍的能工巧匠，他和自己的女儿麦姬都是爱书之人。然而这一家的女主人却神秘失踪，这会儿又有奇怪的人跑来抓他们。莫特带着女儿躲避到一位老朋友家中暂住......

ELINOR: I'm so glad you've finally made your way back here, Mortimer. My poor books are in a terrible state of disrepair.
Mortimer: Don't worry. I'll take care of it.
ELINOR: Don't play with your food, child. You're not a toddler. Look at her, she's as thin as a soap bubble. Oh, she so reminds me of her mother. Not just when she opens her mouth, if she ever does. Speaking of...
Mortimer: We haven't heard from her, if that's what you mean.