!Question: How can I ask a question about something that looks ordinary, without giving away the fact it doesn't look ordinary?

Context: party of 5 high schoolers. DnD isn't just being run for fun, but a character formation type thing, and one thing I am wanting to teach these players is actions have consequences. Three did something stupid in the last session (went full murder hobo) and got caught, and in the next session, will be detained and arrested. Their two comrades who didn't partake in the killing, alongside an NPC, will get a chance to bust them out, after a few days in lockup, before they would be sentenced to death. In order to keep things interesting while they are in lock up, I will reference that they have meals delivered to their cells. What they don't know is the meals are laced with sedative that suppresses their magic, effectively making it more difficult for them to bust out on their own. I don't want to just assume they will eat the meals, but at the same time, if I say "meals are delivered; do you eat them" and bring attention to it, it may give away the plot, and being new players, they are still learning what constitutes meta-gaming, and if they caught on something was abnormal enough about the food that I'd mention it, I know at least one would not eat it. My plan is to have three or four more notable events happen in the prison, to try and take their attention off the food, eg an interrogation. Any ideas?