There are many subtle nuances in speech and conversation that might simply be lost on a person with Asperger’s, thereby making it difficult for them to communicate.
For example, many people with Asperger’s can struggle to recognize or appreciate humor. They might also struggle with sarcasm and therefore take things very literally.
This can potentially come across to others as being dense, or it might appear that the individual is very earnest and honest. They can also lack other nuances in conversation such as pitch that might change the meaning of words.