Silent letters

I wrote some words with silent letters on a little, children's blackboard. I used one of them to do so, name chalk.
The 7esl site Laurie linked to misses one word, worsen. The e is considered silent, as far as I know. But probably it is as the word often. I frequently hear people pronounce the t.
By the way, what about loud letters that do not appear in a word? Like the famous BE word lieutenant. Where is the "f"?
Thanks to laurie54 for hosting the Mono Monday challenge.