They Know When To Eat $20.00 Inside Message Inside: they know how to fly Packages of Heartstrings® cards are shrink-wrapped and sold in sets of 10 cards with envelopes. The actual card size is 4 1/4" x 5 1/2". They Know When To Eat quantity Add to cart SKU: 1224. Categories: Hearts, Sympathy - Healing. Related Products Each of Us Makes a Ripple $20.00 I Only Have Irises for You $20.00 Squeeze the Day $20.00 Champagne $20.00