Animals can be reborn as humans. Although it's difficult for most animals to do many positive actions — it's hard to teach a dog to meditate or to offer community service — it is possible. For this reason, Tibetans take their animals when they circumambulate holy monuments in order to put good imprints on the animals' minds. Many people enjoy saying their prayers or mantras out loud so their pets can hear them and be exposed to such soothing sounds, even though the animals to not understand the meaning.

Thubten Chodron, Buddhism for Beginners