I find retching cats usually present last thing in an evening surgery, leaving you with that tricky choice of whether to anaesthetise and investigate immediately, or delay until the next morning.
It also seems to be the ones you delay (because they’ve eaten, of course) that do have a grass blade while, more often than not, the ones you investigate there and then don’t.
A young colleague showed me a nifty way of elevating the soft palate with a spay hook, which neatly reveals the presence of grass (or not, as the case may be).
Some careful work with the crocodile forceps and you can usually whip out the offending blade of grass very easily.
Definitely a technique I’d recommend.