When Rand sets up the Farm for training he mentions to Taim to be on the lookout for anyone who learns to quickly, that he could possibly be Forsaken. Taim looks disturbed at this because, we assume, he doesn't like the idea of Forsaken on the loose. Unless he is Forsaken and he looks that way because he is wondering if he has been found out. In LoC, The Black Tower, Rand is telling Taim to use Gateways to find men quicker. He then says to himself, without realizing what he is thinking, that Taim learned quickly to Travel, in fact the first time he was shown. Rand again mentions to watch for those who learn to quickly, which Taim did. Another thing, Demandred was always second best to Lews Therin. In fact the Guide mentions Demandred would have been the acclaimed one if Lews Therin wasn't around. Again in the Chapter The Black Tower, Rand is giving his speech and says "I guess I was the first Asha'man", he looks at Taim and continues "That would make you second to me". Taim is furious then and Rand has no idea why Taim is in a snit.