Why is exit status -11 returned?

I'm writing a python script to check a C program I made. Sometimes, when calling my executable from the script, I get

subprocess.CalledProcessError: Command Command '['./parallel_snake', 'input/input1', 'output/output1', '20000']' returned non-zero exit status -11 

This is the line where I call the executable:

p = subprocess.check_output(["./parallel_snake", "input/" + input_file, "output/" + input_file.replace("in", "out"), "20000"])

Why do I get this error, and how can I get rid of it?