I sometimes catch people out. When people come round I normally put a clean towel in the bathroom but sometimes I remove the old one but forget to put the new one in.
Twice, amazingly, someone has emerged from the bathroom after their visit, and I just straight up said, "what did you dry your hands on?" and quick as a flash they go "the towel" then the question sinks in and they realise that the question must have been for a reason and instead of just going "ok, you got me, I'll wash my hands" they stutter around trying to come up with a feeble excuse, like "errr, I mean, there was no towel, I dried my hands on my pants" but by now you already know they are lying and didn't even notice the missing towel because they didn't even consider washing their hands.
Twice, amazingly, someone has emerged from the bathroom after their visit, and I just straight up said, "what did you dry your hands on?" and quick as a flash they go "the towel" then the question sinks in and they realise that the question must have been for a reason and instead of just going "ok, you got me, I'll wash my hands" they stutter around trying to come up with a feeble excuse, like "errr, I mean, there was no towel, I dried my hands on my pants" but by now you already know they are lying and didn't even notice the missing towel because they didn't even consider washing their hands.