I ate out at Chili’s last week and was served a moldy sandwich twice. The second time it was on the bottom and I ate it half of it before I noticed.

You can threaten to sue. Looking ahead though, it may be difficult and expensive to actually win this case, assuming you do sue and push it all the way to trial: you'd have to prove you received the moldy sandwhich from the Chili's--is there any evidence other than your word? (Did you take a cell phone camera picture of the sandwhich? Were you dining with friends or family who'd be witnesses? Etc.) Then you'd have to prove the injury--the feeling of axiety and sickness after eating--which is always tougher to do with a mental injury than a physical one, like a broken arm.

What you might want to do is to send a letter (with some evidence you sent it, like registered mail or fed ex with a tracking #) to both the local management and the central/corporate office of the franchise (legal department or president's office), explaining what happened and how you suffered, AND the fact that the local restaurant has not even shown you the courtesy and respect of responding. Let them know you are seriously contemplating suing and see if they do offer to give you something in compensation.

Either at the same time or after you get an unfavorable response, you should go to a personal injury or product's liability attorney, one will do a free initial consultation, and find out what (s)he thinks you could recover; the odds of winning; and the costs, including what's called "discovery" and also expert fees, it would take to bring the case. That would let you make an informed decision as to whether or not to carry through with a lawsuit if the company does not compensate you voluntarily.