What bus should I take home

A father and his small son were standing in front of the tiger's cage at the zoo. The father was explaining how ferocious and strong tigers are, and junior was taking it all in with a serious expression.

Dad," the boy said finally, "if the tiger got out of his cage and ate you up ..."

"Yes, son?" the father said expectantly.

"What bus should I take home?" the boy finished.