Aha. I posted this about three years ago.
This air resistance will heat the reindeer in the same way that spaceships are heated up when they re-enter the earth's atmosphere. According to our calculations, the lead pair of reindeer will absorb 14.3 quintillion joules of energy per second each.
This means they will burst into spectacular, multicoloured flames almost instantaneously, exposing the reindeer behind them.