grover finds a statue that “looks like my Uncle Ferdinand!” which means this place is giving him some real wack vibes. grover also smelled monsters, which is a big clue that Aunty Em might be a monster herself. percy even narrates these words, “Go ahead, call me an idiot for walking into a strange lady’s shop like that just because i was hungry, but i do impulsive stuff sometimes.” percy is literally saying it’s a bad idea to go into some strangers shop and eat food from them, most likely for safety reasons. percy even said aunty me locked the door behind them as they came inside, if that doesn’t scream murderer idk what does. also the meal was free, like who gives out free food without it being messed with. also a BIG hint is aunty em didn’t even eat anything. i really hope i helped