Brothers or Friends?

The boys were goofing off while we waited in line to pay for their swim team suits. They found a big mirror and made funny faces into it, cracking each other up. Then they counted down 3-2-1! and made scary faces to see who could come up with the best one. They were giggling  like crazy and leaning close to whisper to each other. The cashier saw them and smiled. He turned to me and asked "Are they brothers or friends?" "Both", I replied.