Odd integers are true; even integers are false.
Arrays can be indexed with () or . This leads to namespace problems with functions which are also called with (). For example:
error: undefined variable a.
If you want to call function a, you have to forward declare it for this reason.
There's a different syntax for procedures (which don't have a return value) and functions (which do).
It is required to assign the result of a function to something. You have to write
dummy = foo(1,2,3)
will give an error.
Most of the time, a single element array is treated the same as a scalar. But not always, and not being very careful will lead to weird errors.
There are no zero length arrays.
An array can be length 1; a multidimensional array can be length [1,2,2], but a multidimensional array cannot be length [2,1,1]. If the last dimension has length 1, it simply vanishes to a smaller dimension, unless already 1 dimensional. Example:
a = make_array(1,2,2)
; a has dimensions [1,2,2]
a = make_array(2,1,1)
; a has dimensions 
This means special code must be written to handle any array operations that might end with last dimension 1.
Array slices are weird.
b = a[3,*,2]
means to take a slice of a along the second dimension. I'd expect the answer to be 1 dimensional, since there's only 1 scan in the slice. But the result has dimensions [1,3]
On the other hand, a[3,2,*] has dimensions [1,1,3], and a[*,3,2] has dimensions . It makes sense in a convoluted way, but it sucks.