diff --git a/TODO.md b/TODO.md
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@@ -48,4 +48,6 @@ Function | Matlab output | R output
 
 # Wanna help debugging?
 
-If you find an error, one of the first things to try is to compare the R code with its MATLAB equivalent, which you can find [here](matlab).
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+If you find an error, one of the first things to try is to compare the R code with its MATLAB equivalent, which you can find [here](matlab). Some common causes are:
+
+1. Using `()` to subset an object in R. R uses `[]` for that, whereas Matlab uses `()` for both function calling and object subsetting. Therefore, often objects will be mistakenly interpreted as functions by R due to improper translation.
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