'On' is part of the verb: it's a phrasal verb 'to rely on'. The meaning is 'to depend on'
A pun is a kind of joke where the humour comes from the sound of a word, or perhaps from a double meaning of a word. For example: The violinist played his A's with ease. This means he played the note A easily. But the joke is that the word 'ease' sounds like E's; so it sounds as if the violinist played the note A with a note E.Suggest edit