Hedging his bets

At the merest suggestion that we might be going walkies, Merlin brings me a shoe - I take it and say 'fetch the other one' and he does. Today I was in the bathroom and when I came out I discovered this in the bedroom doorway. Obviously he was unsure which shoes I wanted so he fetched one of each! Whichever one I chose he would go and fetch the matching one. The others just sat and watched - they never fetch anything except a ball or toy.