diff --git a/01-02-setup.Rmd b/01-02-setup.Rmd
index 48a4e53..d15a9ad 100644
--- a/01-02-setup.Rmd
+++ b/01-02-setup.Rmd
@@ -21,6 +21,7 @@ install.packages(c(
   "gprofiler2",
   "ggupset",
   "ggtangle",
+  "ggridges", # needed by enrichplot::ridgeplot()
   "msigdbr",
   "ontologyIndex",
   "WebGestaltR",
@@ -29,6 +30,8 @@ install.packages(c(
 ))
 ```
 
+**Note on `WebGestaltR`:** it includes Rust source code that gets compiled during installation, so a working Rust toolchain (including `cargo`) is required beforehand. If installation fails with a "cargo command is not available" or similar error, install/update Rust via [rustup](https://www.rust-lang.org/tools/install) rather than an older distro-packaged `cargo`, then retry `install.packages("WebGestaltR")`.
+
 <p>&nbsp;</p>  <!-- insert blank line -->
 
 ## Bioconductor packages
diff --git a/08-2-stringdb.Rmd b/08-2-stringdb.Rmd
index d96c243..bdcf5f2 100644
--- a/08-2-stringdb.Rmd
+++ b/08-2-stringdb.Rmd
@@ -215,6 +215,8 @@ sema3a <- string_db$mp("sema3a")
 string_db$get_interactions(c(crabp2, sema3a))
 ```
 
+An empty data frame here is expected, not an error: `CRABP2` and `SEMA3A` are not annotated as directly interacting in STRING, so there is no row to return. `get_interactions` only reports edges that exist directly between the queried proteins; it will not tell you about shared partners or indirect paths between them.
+
 ### Interaction partners
 
 To retrieve the first-shell interaction partners of one or more proteins from the locally loaded network, use `get_interaction_partners`. The output has the same structure as `get_interactions`.