upset.  Could have broken teeth, etc.  My son was less than 2 years old.  (no where near the same thing with your son)

Sometimes kids don't understand the extent of their actions.  They just do what pops into their head.  After calming down.  We talked about why she did it (she didn't really know, she just wanted to) and we talked about what would be a fair punishment/consequence.  She dreaded the idea of the punishment and was crying.  

Since this was a one-off type of situation we then took a different course.  We talked about Jesus.  About his atonement.  About mercy.  We explained that though sometimes we really deserve a punishment.  Sometimes mercy is so much better and that I know she felt bad about this and normally wouldn't do it.  And she is such a good girl.  We would let mercy have it's moment.  But let's be sure to not do it again in the future.

For us it was a good teaching moment and love prevailed.  She's never done something like that again.