O onun ne söylediğini anlayabiliyor gibi görünmüyor.
- He does not seem to be able to catch on to what she is saying.
O onun ne dediğini anlayabiliyor gibi görünmüyor.
- She doesn't seem to be able to catch on to what he is saying.
He didn't have to explain; I caught on right away.
It's a crummy idea, and I certainly hope it does not catch on.