Use things like else in expect block of expect script

In expect block of expect script like as below:

expect {  
    "matched_string" {puts "string is matched"}  
    "I want to get strings else" {puts "string is unmatched"}  #(1)  
}  

At the (1), I want to get all strings which difference with "matched_string". It is same as "else".I can solve with the default or timeout but I don't want to wait.

How can I do it?

Many thanks.