animalsay: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/animalsay - from package: cowsay

You may install the required package with command yum install {package}

Error in other languages:
animalsay: bevel nie gevind nie
animalsay: comandă negăsită
animalsay: comando não encontrado
animalsay: commande introuvable
animalsay: command not found
animalsay: käsku ei ole
animalsay: không tìm thấy lệnh
animalsay: komanda nerasta
animalsay: Kommando nicht gefunden.
animalsay: kommandot finns inte
animalsay: komut yok
animalsay: nie znaleziono polecenia
animalsay: níor aimsíodh an t-ordú
animalsay: no se encontró la orden
animalsay: no s'ha trobat l'ordre
animalsay: opdracht niet gevonden
animalsay: parancs nem található
animalsay: perintah tidak ditemukan
animalsay: príkaz nenájdený
animalsay: příkaz nenalezen
animalsay: команда не найдена
animalsay: командата не е открита
animalsay: 命令找不到
animalsay: コマンドが見つかりません