diff --git a/missing-values.Rmd b/missing-values.Rmd
index ad266d3..d872e59 100644
--- a/missing-values.Rmd
+++ b/missing-values.Rmd
@@ -221,6 +221,7 @@ health |>
 
 Summary functions generally work with zero-length vectors, but they may return results that are surprising at first glance.
 There's almost always some deeper logic behind them.
+
 A sometimes simpler approach is to perform the summary and then make the implicit missings explicit with `complete()`.
 
 ```{r}
@@ -237,3 +238,29 @@ health |>
 ```
 
 Main con of this approach is that you need to carefully specify the `fill` argument so that
+
+## NaN
+
+Special not a number.
+In general it behaves like an `NA`:
+
+```{r}
+x <- c(NA, NaN)
+is.na(x)
+is.nan(x)
+```
+
+You get these from mathematical operations that don't have a well defined answer
+
+```{r}
+0 / 0 
+0 * Inf
+Inf - Inf
+sqrt(-1)
+log(-1)
+```
+
+```{r}
+sqrt(-1 + 0i)
+log(-1 + 0i)
+```