Accidently discovered what a bit of heavely incentive does, this afternoon. I gave him the choice of 2.3 miles, or a bit shorter & to try a bit faster; he chose the second one. I thought the sky looked clear enough, and we set off, a bit of thunder two to three miles away on the outward leg. Towards the end of the return leg it became obvious that the weather was getting rapidly worse, and about a quarter of a mile from home the rain started. His speed picked up noticeably, and he was duly congratulated on his return to home; he had a big grin on his face.