Remember that reflexive verbs need a reflexive pronoun to use (me, te, se, nos, os). It depends on who the verb falls to, a different reflexive pronoun will be used.
As the verb "cepillarse" and "divertirse" are reflexive, they must be added after the verb when the form of the verb is <u>impersonal</u> (infinitive, gerund and participle). In this case "-se".