Unable to run whalesay demo

After running the Docker provided command below to run the whalesay demo program,

sudo docker run docker/whalesay cosway boo

I get the following error:
docker: Error response from daemon: invalid header field value “oci runtime error: container_linux.go:247: starting container process caused “exec: \“cosway\”: executable file not found in $PATH”\n”.

I have just installed Docker and am very new to this! My environment is:
Ubuntu Linux 14.04 LTS
Kernel 3.13.0-100-generic
docker-engine 1.12.2-0~trusty; architecture amd64



That error pretty much means what it says. (Did you mean “cowsay”?)

Yep, I should have typed cowsay! Thanks for the second pair of eyes.