You see that a lead has an unusually high amount of Clicked Link activity for a particular email after delivery.
There can be a couple reasons for this. If you see that all links in the email are being clicked immediately upon delivery, it is likely that the lead's email security software is link-testing to guard against phishing or malicious links. However, if you see an unusually large number of link clicks over the course of a day or two, it may be that the lead forwarded the email to other people who clicked on the links. Since the tracking links are specific to the lead who was sent the original email, if the email is forwarded to other people, their clicks will be recorded under the initial lead's activity history.
Marketo does not have a way to confirm this is the case, but if you open the Click Link activities in the leads Activity Log and look at the details, you may see the User Agent (which indicates the operating system and client software used to display the email) is different for each click. If you see a variety of different user agents in the details, it is likely the email is being opened and clicked by different people who were forwarded the email.