Why can't my Nikon D3100 detect red eyes?

I just can't figure It out. The red is clearly visible and when I try to fix it, it just says unable to detect red eyes. Any tips? NEW to SLR and have read manual. Still confused.

In-camera processor correction of red eye may just not work very well. Maybe software editing could do better, maybe not. The best thing is to avoid it by using an external flash as bounce flash.

If you want to avoid redeye, you need to use an external flash mounted on a flash bracket.

Most modern photo programs have an automatic redeye removal feature, so you can do all that in post if you don't have an external flash or flash bracket.