I can't see the whole exercise, but I guess you have to mix two "frases hechas", so you can say "A caballo regalado, buena sombra le cobija" which is a mix of 2 Spanish "frases hechas" (I don't remember the word in English, sorry): "a caballo regalado no se le mira el diente" and "a quien buen árbol se arrima, buena sombra le cobija"
