Zoom-zoom.

Shares of last week's IPO darlings Pinterest (PINS) and Zoom (ZM)  both zipped higher on their second day of trading Monday afternoon as investors digested the longer-term prospects of both companies.

Shares of Pinterest were up 4.5% to $25.50 in mid-afternoon trading on Monday, while shares of Zoom recovered from early losses and were up 7.4% at $66.60. Earlier they were down more than 2.3% at $60.60.

The two tech unicorns that went public on Thursday closed well above their initial public offering prices, with Pinterest up 28.4% and Zoom up 72.2% on their first day of trading. On Wednesday, Zoom priced its shares at $36 while Pinterest set a price of $19 per share.

But, as Jim Cramer noted on Thursday on Cramer Live, TheStreet's daily live show on Facebook and TheStreet.com, it's the second day of trading that investors need to keep a watchful eye on.

Pinterest, based in San Francisco, is an "image discovery" service, which means that its users, who number more than 250 million, post images of things they find interesting on its site. Others can then peruse those collections, resulting in a kind of curated image directory of things.

Zoom, based in San Jose, is a video service built on top of cloud computing facilities. It's meant to be a more modern version of services that have been around for decades, such as Cisco Systems' WebEx or the ubiquitous Polycom conference room video systems.

Read: A Primer for the Pinterest Public Offering on Thursday