system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do you get caught counting cards?

How does a casino catch someone counting cards if the method behind it is keeping a count in your head, completely hidden from the eyes of the casino? 

Edit: How often do casinos actually call people out on counting? Do they have to have real evidence or can they just kick you out on a hunch?
gpt
You can tell by the way someone is betting.  When the situation is favorable based on the count, that's when you want to start betting heavy.  Also, card counters often work in groups and so if additional people start showing up at the table and everyone is betting heavy, it's a pretty good indicator that something's up.