diff --git a/README.md b/README.md
index 5a14dec..0820bd0 100644
--- a/README.md
+++ b/README.md
@@ -1,18 +1,16 @@
-# sandworm
-program space is an arbitrary sized grid
-the worm starts where you place the worm head @
-as it passes over commands, they get moved to the back of the worm (also depending on the worm length)
-commands to change direction <>^v
-values get pushed to stack (eaten) when passed over, worm body length increases
-autosarkophagy/self-cannibalism is possible, cutting off the back of the worm (the lower part of the stack) and pushing the passed value to the stack (front of worm)
-conditional: pop then side/forward if top of stack is zero
+# Stupid Worm Languag
+- program space is an arbitrary sized grid
+- the worm starts where you place the worm head @
+- as it passes over commands, they get moved to the back of the worm
+- values get pushed to stack (eaten) when passed over, worm body length increases
+- the program gets rearranged every time the worm executes it
 
 ## commands
 ```
 +- pop 2 values *, push sum/difference (uses the order they are popped, so `0 -` negates the top of the stack)
 ><^v change direction
-0123456789ABCDEF push number to stack
-/\ pop stack, reflect to the side if zero
+0..9 push number to stack
+/\ pop stack, reflect to the side if not zero
 ? reads one byte of input
 = duplicate top of stack
 ! pop and write output as ascii char
diff --git a/src/main.rs b/src/main.rs
index ae86212..41b3570 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -159,20 +159,19 @@ impl SandWormInterpreter {
 				self.worm_in.push(instruction - 48);
 				dont_push_instruction = true;
 			}
-			// b'0'..=b'9' => self.grow(instruction - 48),
 			b'+' => {
 				let a = self.shrink();
 				self.worm_out.push(instruction);
 				let b = self.shrink();
 				dont_push_instruction = true;
-				self.worm_in.push(a + b);
+				self.worm_in.push(a.wrapping_add(b));
 			}
 			b'-' => {
 				let a = self.shrink();
 				self.worm_out.push(instruction);
 				dont_push_instruction = true;
 				let b = self.shrink();
-				self.worm_in.push(a + b);
+				self.worm_in.push(a.wrapping_sub(b));
 			}
 			b'v' => self.direction = Direction::Down,
 			b'^' => self.direction = Direction::Up,