A friend of mine, also a Japanese student, thought I'd like this expression.
She was right! (Hi Vera chan!)
Reading: awa wo kuu
Meaning: to be confused
Literally: eat a bubble
Wait... eat a bubble?! I'm confused now...:P
For some reason, this makes me think of the situation when someone is talking or doing some other mouth opening activities and then a soap bubble enters his mouth, a split second before he closes his mouth on it. The bubble bursts inside his mouth and he now faces the reality of tasting soap. Now, there is that split second of not knowing what is the proper procedure to continue with...
"Should I spit it out? should I just not make a big deal out of it? should I laugh...did I just eat a bubble!?"
I can totally see how that split second of being frozen in time and not moving any jaw muscles, symbolizes confusion.