its not really theft if the bus driver lets you on is it? There is no way anyway you would get in trouble for it.

the point is that by attempting to touch in first and failing, it would then seem more credible at the end when you find the other card that works. It looks more like an honest mistake than trying first with cash and then producing a card. Tho that would also work tbh

If u really cant be bothered to pay for the bus, especially if u only going a few stops, then there is a trick which works about 50% of the time! For best results What u need is an empty oyster card, a topped up oyster card and a £10 note. When entering the bus, touch in your dead card, then offer the driver the tenner... Often they wont have enough change and if not then they will often just let you on. If they refuse to let you on, complain for a bit, say your only going a few stops or whatever and then they might let u on. If they refuse to let you on (which isnt really nice on the basis they dont have enough change) or start digging to get you your change... then touch in your live oyster card if u have one! (and say "oh wait here it is! Sorry) Doesn't always work, but you got nothing to lose by trying